Updated

Russian President Vladimir Putin backed Ukraine's cease-fire plans Saturday and appealed to both sides to halt all military operations.

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.

Poroshenko bills the weeklong cease-fire as the first step in a wider peace plan that would include an amnesty for pro-Russian separatist fighters.

Putin said however that without action directed at starting talks, the plan was "not viable and unrealistic."

Ukrainian troops have struggled 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.

The 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 Europe have placed targeted financial sanctions on some Russian officials but have held off on targeting entire economic sectors.

It has been unclear whether Russia can or will influence the fighters to de-escalate the conflict. Putin consulted with Poroshenko several times by phone on the cease-fire, but Russia's foreign minister earlier Saturday had criticized it sharply as an "ultimatum" to rebels.

The more conciliatory tone of the Kremlin statement contrasted with Putin's move Saturday to order military forces in central Russia to observe a 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 Defense 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, while nine Ukrainian service members were wounded in clashes just before and after the cease-fire began Friday.

Otherwise, no large-scale fighting had been reported Saturday, the first full day of what is to be a six-and-a-half-day stand-down by the Ukrainian military.