MINSK, Belarus — Ukraine, Russia and the Kremlin-backed separatists signed a cease-fire deal Friday after five months of bloodshed, and Europe readied additional sanctions on Moscow. NATO leaders created a new force designed to prevent any aggression by Russia against alliance members.

Gunfire and shelling appeared to fall silent across eastern Ukraine shortly after the appointed hour, to the relief of war-weary residents. But the U.S. voiced skepticism that the rebels and Russia would stop violating Ukrainian sovereignty.

Ukrainian President Petro Poroshenko said he ordered his forces to halt hostilities at 6 p.m. (11 a.m. EDT) after the deal was signed in Minsk, the Belarusian capital, by all three sides and a representative of the Organization for Security and Cooperation in Europe. Separatist leaders also said they ordered their forces to hold their fire.

Poroshenko said the cease-fire was based on an agreement reached during a “long conversation” with Russian President Vladimir Putin and would be watched over by international monitors from the OSCE.

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, Heidi Tagliavini of the OSCE told reporters in Minsk.

Mikhail Zurabov, the Russian ambassador to Ukraine who also signed the deal, described the exchange of lists of more than 1,000 prisoners from each side as a “breakthrough.” Poroshenko said a prisoner exchange could begin as early as Saturday.

President Obama said he was hopeful the cease-fire would hold but skeptical that the rebels would follow through and that Russia would stop violating Ukraine’s sovereignty and territorial integrity.

“It has to be tested,” Obama said at the close of a two-day NATO summit in Wales.

Keeping the pressure on Moscow, European Union ambassadors gave preliminary approval Friday night to new Ukraine-related sanctions on Russia involving access to capital markets and trade in arms and defense technology, dual-use goods and sensitive technologies, an EU diplomat said.

NATO leaders at the summit also approved plans to create a rapid response force to counter Russian aggression, with a headquarters in Eastern Europe that could quickly mobilize if an alliance country were to come under attack. Ukraine is not a NATO member, but the entire alliance has been alarmed by Russia’s actions in Ukraine, and Russia is under both U.S. and EU sanctions for its support of the rebels.