The cease-fire in Ukraine's rebellious east appears to be holding, despite some violations early on, the head of the country's national guard said Saturday.

National Guard Commander Stepan Poltorak was quoted by the Interfax news agency as saying that although some shooting took place up to about 45 minutes after the cease-fire, "as of this morning there haven't been any violations, either from our side, of course, or from the terrorists."

In Donetsk, the largest city controlled by the Russian-backed separatists, the night passed quietly — a rarity after several months of daily shelling in residential areas. As of Saturday morning there were no reports of shooting or shelling, the mayor's office said in a statement, though some shelling could be heard in Donetsk late Friday afternoon.

Ukraine, Russia and the Kremlin-backed separatists signed the cease-fire deal Friday in Minsk, the Belarusian capital. The negotiators also agreed on the withdrawal of all heavy weaponry, the release of all prisoners and the delivery of humanitarian aid to devastated cities in eastern Ukraine.

If the ceasefire holds, it would be a landmark achievement for both sides. Fighting between pro-Russian rebels and Ukrainian government troops, which is dragging into its fifth month, has ravaged the already teetering Ukrainian economy, claimed at least 2,600 civilian lives and left hundreds of thousands homeless, according to United Nations estimates.

But Western leaders voiced skepticism over Russia's commitment to the deal. A previous 10-day cease-fire in June, which each side repeatedly accused the other of violating, yielded few results at the negotiating table.

U.S. President Barack Obama said he was hopeful the cease-fire would hold but unsure the rebels would follow through and that Russia would stop violating Ukraine's sovereignty and territorial integrity.

"It has to be tested," Obama said Friday at the closing of a two-day NATO summit in Wales.

Both the U.S. and the European Union have prepared even tougher sanctions on Moscow, and Obama stressed that the most effective way to ensure the cease-fire's success was to move ahead with those measures and maintain pressure on Russia. According to an EU diplomat, these new measures would target Russia's access to capital markets and trade in arms and defense technology, dual-use goods and sensitive technologies. The new sanctions were given preliminary approval Friday night and could be implemented as early as Tuesday.

"If certain processes get underway, we are prepared to suspend sanctions" against Russia, German Chancellor Angela Merkel said.

Ukraine, NATO and Western nations have accused Russia of backing the separatists with weapons, supplies and thousands of regular troops. Moscow has denied this, but a NATO military told The Associated Press that the number of Russian soldiers directly involved in the conflict has grown past the alliance's earlier estimate of at least 1,000.

In a statement published online Saturday, Russia's foreign ministry condemned further EU sanctions and promised that "there will undoubtedly be a reaction from our side" to any new measures. In August, Russia passed a sweeping ban on meat, fruit, vegetables, and dairy product imports from the EU, the U.S. and a host of other countries who imposed sanctions on Russia.