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OTTAWA -- Prime Minister Stephen Harper arrived in Eastern Europe late Tuesday still throwing political punches at Russia's Vladimir Putin as he announced a surprise visit to Ukraine.

Harper returns to Ukraine on Saturday to attend the swearing in of the country's new president-elect, Petro Poroshenko, adding to an already packed European itinerary.

The Ukraine visit was made known to travelling news media on Harper's aircraft after it became airborne from Ottawa to Warsaw.

Harper, who also visited Ukraine in March, said he wants to show Canada's support for that country's aspirations for prosperity and stability.

"The people of Ukraine deserve a government that defends the country's political and territorial integrity against those who would seek to control it once more," he said in a written statement distributed on the plane.

"I look forward to travelling to Ukraine to witness the swearing-in of president-elect Petro Poroshenko and to offer the people of Ukraine Canada's full support as they take important steps to restore stability and prosperity."

The prime minister did not interact with the journalists travelling with him on the eight-hour transatlantic flight.

Harper meets early Wednesday with Polish Prime Minister Donald Tusk to discuss the Ukraine crisis.

Marcin Bosacki, Poland's ambassador to Canada, said his government wants to see NATO's eastern flank strengthened militarily because of Russia's unprecedented violation of Ukraine's borders.

"Yes, we do propose establishing permanent NATO bases in Poland and in the eastern part of the alliance," Bosacki told reporters on Harper's plane.

"We would be happy for bigger assistance, but it's up to the Canadian government."

Several dozen Canadian military personnel are still doing exercises in Poland with paratroopers from his own country and the United States, he said.

Canada has also sent a frigate to join NATO's standing task force in the eastern Mediterranean Sea, and six CF-18 jet fighters to Romania, in addition to the troops from the 3rd Battalion Princess Patricia's Canadian Light Infantry sent to Poland to participate in a land exercise.

Poland views Canada as one of its closest NATO allies, while Harper and Tusk are like minded on Russia and Ukraine, said Bosacki.

Harper has labelled Putin a threat to world peace after Russia annexed the Crimean Peninsula, and for instigating the continuing unrest in eastern Ukraine.

Earlier Tuesday, U.S. President Barack Obama arrived in Warsaw with a pledge of more American military assets to Europe, and said he would ask U.S. Congress for $1 billion to support the effort. The U.S. also wants to bolster non-NATO countries in Europe that border Russia, including Ukraine, Georgia and Moldova.

Polish President Bronislaw Komorowski responded by saying that Poland's defence spending would be increased to two per cent of GDP, the desired financial target that the 28-country NATO military alliance has set.

That would make Poland only the sixth NATO country to reach that target, and put it well ahead of Canada, whose current defence spending stands at one per cent of GDP, a decline from 1.2 per cent during the war in Afghanistan.

Harper is making the first stop of a European tour that includes a celebration of the end of the Cold War in Poland, the G7 summit in Belgium and the 70th anniversary ceremonies of the Normandy invasion in France.

Last week, Harper lambasted Putin in speech that linked him with the worst evils of 20th century communism, which he called a ruthless and "poisonous ideology" that "slowly bled into countries around the world."

Harper will join Obama and other world leaders in Warsaw on Wednesday to mark the 25th anniversary of Poland's emergence from communism in a major ceremony attended by some three-dozen world leaders.

They will be marking June 4, 1989, the day Poland's anti-communist Solidarity movement officially won power in democratic elections.

Harper's unyielding anti-Putin rhetoric struck a harsher tone compared with Obama's remarks earlier in the day in Warsaw.

France has invited Putin to Friday's D-Day ceremonies, but Harper has made it clear he does not want to speak to the Russian leader.

Obama said if he happens to run into Putin later in the week in France he would do what he could to dial down the current tensions. But the president also made clear the U.S. was prepared to impose other punitive measures if necessary.

"We are interested in good relations with Russia," Obama said. "We are not interested in threatening Russia."

In Warsaw, Harper will see a vibrant Poland, an Eastern European success story, outpacing economically hobbled Ukraine, which is still struggling to break from the influence of Russia.

"Not many people know that in 1990 our GDP was actually equal to the Ukrainians, and now it's three times," said Bosacki.

Both of Harper's visits will resonate in Canada among the nearly million Canadians of Polish descent and the 1.2 million of Ukrainian descent.

On Thursday, Harper is in Brussels to attend the G7 summit, which was cobbled together to replace the planned G8 gathering in Sochi, Russia that has since been scrubbed after the crisis in Ukraine.

Harper has said he will use the Brussels meeting to lobby fellow leaders for more money for his signature initiative on maternal and child health.

The uncertainty surrounding the lack of a final text of Canada's ambitious free- trade deal with the European Union will also hover over Harper as well on Thursday, but no progress is expected.

Harper came to Brussels with great fanfare last October to sign an agreement in principle with European Commission President Jose Manuel Barroso. But the deal has since stalled, while the EU is focusing on a new round of talks with the United States.

An aide to Harper, who spoke on the condition of anonymity, said it was unlikely the Harper and Barroso would talk trade Thursday in Brussels, even though both leaders would see each other at the G7 meeting.

Harper also wants to talk about jobs and the global economy at the G7, but the Ukraine and Russia situation is likely to overshadow that.

Harper moves on to Normandy on Friday, where he will attend a series of ceremonies to mark the D-Day invasion, the turning point that helped secure the Allied victory in the Second World War.