KYIV, UKRAINE -- Russian President Vladimir Putin ordered a partial mobilization of reservists Wednesday to bolster his forces in Ukraine, a deeply unpopular move that sparked rare protests across the country and led to almost 1,200 arrests.

The risky order follows humiliating setbacks for Putin鈥檚 troops nearly seven months after they invaded Ukraine. The first such call-up in Russia since World War II heightened tensions with Ukraine鈥檚 Western backers, who derided it as an act of weakness and desperation.

The move also sent some Russians scrambling to buy plane tickets to flee the country.

In his 14-minute nationally televised address, Putin also warned the West that he isn鈥檛 bluffing about using everything at his disposal to protect Russia 鈥 an apparent reference to his nuclear arsenal. He has previously rebuked NATO countries for supplying weapons to Ukraine.

Confronted with steep battlefield losses, expanding front lines and a conflict that has raged longer than expected, the Kremlin has struggled to replenish its troops in Ukraine, reportedly even resorting to widespread recruitment in prisons.

The total number of reservists to be called up could be as high as 300,000, Russian Defence Minister Sergei Shoigu said. However, Putin's decree authorizing the partial mobilization, which took effect immediately, offered few details, raising suspicions that the draft could be broadened at any moment. Notably, one clause was kept secret.

Despite Russia鈥檚 harsh laws against criticizing the military and the war, protesters outraged by the mobilization overcame their fear of arrest to stage protests in cities across the country. Nearly 1,200 Russians were arrested in anti-war demonstrations in cities including Moscow and St. Petersburg, according to the independent Russian human rights group OVD-Info.

Associated Press journalists in Moscow witnessed at least a dozen arrests in the first 15 minutes of a nighttime protest in the capital, with police in heavy body armor tackling demonstrators in front of shops, hauling some away as they chanted, 鈥淣o to war!鈥

鈥淚鈥檓 not afraid of anything. The most valuable thing that they can take from us is the life of our children. I won鈥檛 give them life of my child," said one Muscovite, who declined to give her name.

Asked whether protesting would help, she said: 鈥淚t won鈥檛 help, but it鈥檚 my civic duty to express my stance. No to war!鈥

In Yekaterinburg, Russia鈥檚 fourth-largest city, police hauled onto buses some of the 40 protesters who were detained at an anti-war rally. One woman in a wheelchair shouted, referring to the Russian president: 鈥淕oddamn bald-headed 鈥榥ut job鈥. He鈥檚 going to drop a bomb on us, and we鈥檙e all still protecting him. I鈥檝e said enough.鈥

The Vesna opposition movement called for protests, saying: 鈥淭housands of Russian men 鈥 our fathers, brothers and husbands 鈥 will be thrown into the meat grinder of the war. What will they be dying for? What will mothers and children be crying for?鈥

The Moscow prosecutor鈥檚 office warned that organizing or participating in protests could lead to up to 15 years in prison. Authorities have issued similar warnings ahead of other protests. Wednesday's were the first nationwide anti-war protests since the fighting began in late February.

Other Russians responded by trying to leave the country, and flights out quickly became booked.

In Armenia, Sergey arrived with his 17-year-old son, saying they had prepared for such a scenario. Another Russian, Valery, said his wife鈥檚 family lives in Kyiv, and mobilization is out of the question for him 鈥渏ust for the moral aspect alone.鈥 Both men declined to give their last names.

The state communication watchdog Roskomnadzor warned media that access to their websites would be blocked for transmitting 鈥渇alse information鈥 about the mobilization.

Residents in Ukraine's second-largest city, Kharkiv, appeared despondent about the mobilization as they watched emergency workers clear debris from Russian rocket attacks on two apartment buildings.

鈥淵ou just don鈥檛 know what to expect from him,鈥 said Kharkiv resident Olena Milevska, 66. 鈥淏ut you do understand that it鈥檚 something personal for him.鈥

In calling for the mobilization, Putin cited the length of the front line, which he said exceeds 1,000 kilometres (more than 620 miles). He also said Russia is effectively fighting the combined military might of Western countries.

Western leaders said the mobilization was in response to Russia's recent battlefield losses.

President Joe Biden told the U.N. General Assembly that Putin鈥檚 new nuclear threats showed 鈥渞eckless disregard鈥 for Russia鈥檚 responsibilities as a signer of the Treaty on the Non-Proliferation of Nuclear Weapons.

Hours later, Ukrainian President Volodymyr Zelenskyy urged world leaders at the gathering to strip Russia of its vote in international institutions and its U.N. Security Council veto, saying that aggressors need to be punished and isolated.

Speaking by video, Zelenskyy said his forces 鈥渃an return the Ukrainian flag to our entire territory. We can do it with the force of arms. But we need time.鈥

Putin did not attend the meeting.

Following an emergency meeting of European Union foreign ministers Wednesday night, EU foreign policy chief Josep Borrell promised more sanctions on Russia over its escalation of the Ukraine conflict. He said he was certain there would be 鈥渦nanimous agreement鈥 for sanctioning both Russia鈥檚 economy and individual Russians.

鈥淚t鈥檚 clear that Putin is trying to destroy Ukraine. Hes trying to destroy the country by different means since he鈥檚 failing militarily,鈥 Borrell said.

Russian opposition leader Alexei Navalny said the mobilization means the war 鈥渋s getting worse, deepening, and Putin is trying to involve as many people as possible. 鈥 It鈥檚 being done just to let one person keep his grip on personal power.鈥

The partial mobilization order came two days before Russian-controlled regions in eastern and southern Ukraine plan to hold referendums on becoming part of Russia 鈥 a move that could allow Moscow to escalate the war. The votes start Friday in the Luhansk, Kherson and partly Russian-controlled Zaporizhzhia and Donetsk regions.

Foreign leaders are already calling the votes illegitimate and nonbinding. Zelenskyy said they were a 鈥渟ham鈥 and 鈥渘oise鈥 to distract the public.

Michael Kofman, head of Russian studies at the CNA think tank in Washington, said Putin has staked his regime on the war, and that annexation 鈥渋s a point of no return,鈥 as is mobilization 鈥渢o an extent.鈥

"Partial mobilization affects everybody. And everybody in Russia understands ... that they could be the next wave, and this is only the first wave,鈥 Kofman said.

Shoigu, Russia's defence minister, said only some of those with relevant combat and service experience will be mobilized. He said about 25 million people fit that criteria, but only about 1 per cent of them will be mobilized.

It wasn鈥檛 clear how many years of combat experience or what level of training soldiers must have to be mobilized. Another clause in the decree prevents most professional soldiers from terminating their contracts until after the partial mobilization.

Putin's mobilization gambit could backfire by making the war unpopular at home and hurting his own standing. It also concedes Russia's underlying military shortcomings.

A Ukrainian counteroffensive this month seized the military initiative from Russia and captured large areas in Ukraine from Russian forces.

The Russian mobilization is unlikely to produce any consequences on the battlefield for months because of a lack of training facilities and equipment.

Russian political analyst Dmitry Oreshkin said it seemed 鈥渁n act of desperation.鈥

鈥淧eople will evade this mobilization in every possible way, bribe their way out of this mobilization, leave the country,鈥 he said.

He described the announcement as 鈥渁 huge personal blow to Russian citizens, who until recently (took part in the hostilities) with pleasure, sitting on their couches, (watching) TV. And now the war has come into their home.鈥

In his address, Putin accused the West of engaging in 鈥渘uclear blackmail鈥 and cited alleged 鈥渟tatements of some high-ranking representatives of the leading NATO states about the possibility of using nuclear weapons of mass destruction against Russia.鈥

He did not elaborate.

鈥淲hen the territorial integrity of our country is threatened, to protect Russia and our people, we will certainly use all the means at our disposal,鈥 Putin said.

In other developments, relatives of two U.S. military veterans who disappeared while fighting Russia with Ukrainian forces said they had been released after about three months in captivity. They were part of a swap arranged by Saudi Arabia of 10 prisoners from the U.S., Morocco, the United Kingdom, Sweden and Croatia.

And in another release, Ukraine announced early Thursday that it had won freedom from Russian custody of 215 Ukrainian and foreign citizens, including fighters who had defended a besieged steel plant in the city of Mariupol for months. Zelenskyy posted a video showing an official briefing him on the freeing of the citizens, in exchange for pro-Russian opposition leader Viktor Medvedchuk and 55 others held by Ukraine.

鈥-

Yesica Fisch in Kharkiv contributed to this story.

Correction:

A previous version of this story was corrected to show that the Ukrainian presidential spokesman's last name is Nikiforov, not Nikoforov.