People stand at their cars waiting in line to leave Ukraine at the Ukrainian-Russian border checkpoint in Izvaryne, Luhansk region, eastern Ukraine Thursday, June 26, 2014. (Dmitry Lovetsky/AP)

The warring sides in Ukraine’s conflict announced Thursday that they would continue talks Friday, when a shaky cease-fire is set to expire, while Secretary of State John F. Kerry pushed Russia to call within “hours” for rebels in Ukraine to disarm.

The diplomatic efforts came on the eve of a critical day for Ukraine’s future. President Petro Poroshenko plans to sign Friday the same economic deal with the European Union that his predecessor, Viktor Yanukovych, backed out of in November under heavy Russian pressure. That decision set off months of pro-European protests in Ukraine that eventually led to Yanukovych’s ouster and the worst tension between Russia and the West since the Cold War. E.U. leaders also were set to meet Friday to discuss possible new sanctions against Russia.

A cease-fire that has calmed but not ended the violence in eastern Ukraine — where pro-Russian separatists have occupied government buildings and seized territory — was set to end Friday morning. It remained unclear whether Poroshenko would extend the truce, as Russian and European leaders have urged him to do. On Monday, the two sides met for talks for the first time.

But Poroshenko is facing increasing pressure from Ukrain­ian hard-liners to end the pause in hostilities, even as each side has accused the other of violating the truce. Nine soldiers died Tuesday when rebels shot down a military helicopter near the city of Slovyansk, and a Ukrainian base in the Donetsk region came under attack Thursday evening.

Early Friday, in an apparent goodwill gesture, rebels released four of eight observers from the Organization for Security and Cooperation in Europe who were captured in eastern Ukraine over a month ago, the organization said in a statement.

Thousands of Ukrainians in cars stuffed with belongings lined up Thursday at the eastern border to cross into Russia, with some saying they felt betrayed by their government and vowing never to return. (Dmitry Lovetsky/AP)

Poroshenko, speaking Thursday in Strasbourg, France, asked Russia to support his peace plan “with deeds and not just words.” Ukrainian and Western officials have accused Russia of funneling weapons and volunteers across the border into Ukraine. Russia denies the charge.

In Paris, where Kerry was holding consultations with allies on a host of issues, the top American diplomat said the United States and France are “in full agreement that it is critical for Russia to show in the next hours, literally, that they are moving to help disarm the separatists, to encourage them to disarm, to call on them to lay down their weapons and begin to become part of a legitimate political process.”

Kerry had warned a day earlier that without a very public show of Russian support for the Ukrainian peace process, tougher U.S. and European sanctions may be necessary.

Sanctions “need to be ready,” Kerry said. “But our preference is not to have to be into a sanctions mode.”

Gearan reported from Paris.