KYIV, Ukraine -- Russian President Vladimir Putin expressed support Saturday for Ukraine's unilateral cease-fire in its battle against pro-Russian separatists and appealed to both sides to halt all military operations.
But he warned that Ukrainian President Petro Poroshenko's blueprint for peace would not be viable without action to start peace negotiations.
The qualified Russian backing for Poroshenko's effort to halt the conflict was another in a series of shifting Kremlin moves and statements that leave unclear the level of Moscow's commitment to de-escalating the conflict.
Putin's conciliatory words came on the same day he ordered large-scale military exercises that NATO criticized as likely to raise tensions. U.S. officials also accused Russian troops of moving back into positions near the border with Ukraine's troubled east.
The Kremlin said in a statement that Putin "calls on the opposing sides to halt any military activities and sit down at the negotiating table."
The statement said Putin supported Ukrainian President Petro Poroshenko's decision to order Ukrainian troops to observe a unilateral cease-fire starting Friday night.
But it added that Putin wanted to draw "attention to the fact that the proposed plan, without practical action directed at a beginning for a negotiating process, will not be viable or realistic."
Poroshenko bills the unilateral cease-fire as designed to inspire a wider peace plan that would include an amnesty for pro-Russian separatist fighters who disarm.
Further steps would include joint security patrols, a buffer zone on the border, early regional and parliamentary elections, protections for the language rights of people who use Russian as their main language, and eventually changes in the constitution to permit more regional self-government.
Ukrainian troops have struggled for weeks to suppress separatists who have seized buildings and declared independence in the eastern Donetsk and Lugansk regions near the border with Russia.
Ukraine and the United States have accused Russia of supporting the insurgency, including by permitting tanks to cross the border and wind up in the rebels' arsenal. Russia counters that it is not supporting the insurgents and Russians who have joined the fighting are doing so as private citizens.
U.S. and European leaders have called on Russia to play a constructive role in settling the conflict and halt what they say is support for the rebels. The U.S. and European Union have imposed financial sanctions on specific Russian officials but have held off on targeting entire economic sectors.
It remains unclear whether Russia can or will influence the pro-Russian fighters to de-escalate the conflict. Putin has consulted with Poroshenko several times by phone on the Ukraine cease-fire initiative, but earlier Russian statements on the peace plan had criticized it sharply as an "ultimatum" seeking to pressure rebels to disarm.
The more open-minded tone of the latest Kremlin statement contrasted with Putin's move Saturday to order military forces in central Russia to go on combat alert and to launch an exercise for airborne troops.
The combat alert in the central military district, which encompasses the Volga region and the Ural mountains but not western Russia, will last until next Saturday and involve 65,000 troops, Russian Defence Minister Sergei Shoigu said.
NATO spokeswoman Oana Lungescu on Saturday lamented Moscow's military exercises, saying that "it can be seen as a further escalation of the crisis with Ukraine."
Pro-Russian separatists in Ukraine's embattled east have dismissed the cease-fire as fake -- and continued to shoot at Ukraine border positions after the truce began Friday night.
The Ukrainian Defence Ministry said six troops were wounded in attacks on border posts shortly before the truce's start, while three others were wounded in later mortar and sniper attacks on two posts.
Nonetheless, no large-scale fighting was reported Saturday, the first full day of what is to be a 6 1/2-day stand-down by the Ukrainian military ending Friday morning.
In Donetsk, a group of armed men gathered Saturday in the central square to take a military oath to the self-proclaimed Donetsk People's Republic.
Pavel Gubarev, who describes himself as governor of the breakaway republic, said there was no sign of any cease-fire near Slovyansk, scene of serious clashes for several months.
"There is no cease-fire over there," Gubarev said. "There is shooting all the time, and this cease-fire that Poroshenko is talking about is just fake. The Ukrainian forces are either not under his control, or he is just a liar."
Tension between Russia and Ukraine escalated sharply in February when protests in favour of closer ties with the European Union drove pro-Russian President Viktor Yanukovych from power. Russia denounced the events as a coup and annexed Ukraine's mostly Russian-speaking Crimea region. Rebellion in the eastern regions broke out shortly afterward, with Ukraine accusing Russia of supporting it.
