Ukrainian President Petro Poroshenko has announced his government will extend by 72 hours a cease-fire in eastern Ukraine.
The announcement came shortly after Poroshenko returned to Kyiv from Brussels, where he signed a landmark free-trade deal at a European Union summit.
On his website, Poroshenko said the truce had been extended in line with a deadline set by EU leaders for Ukrainian rebels to agree to a mechanism to monitor a cease-fire, return border checkpoints to Kyiv control, and free hostages including four monitors of the OSCE rights and security watchdog.
The truce will now run until 10 p.m. local time on June 30.
Earlier, pro-Russian separatists in eastern Ukraine expressed a willingness to abide by the extended truce.
But Donetsk rebel leader Aleksander Borodai said the separatists would not hand over control of three captured border posts.
Despite the cease-fire, isolated incidents of violence were reported in the Donetsk region on June 28. The military accused the separatists of shooting at soldiers at Kramatorsk airfield. The military said there were no casualties among the troops.
Earlier on June 27 in Brussels, EU leaders warned Russia of fresh sanctions if there was no easing of tensions in eastern Ukraine by June 30.
EU leaders warned that punitive measures have been drawn up and could be levied immediately.
EU leaders also expressed frustration that the weeklong cease-fire announced by Poroshenko had not ended the fighting.
In Brussels at the signing ceremony, Poroshenko said Ukraine had "paid the highest possible price to make her European dreams come true."
Failure to sign the accords last November had sparked the Euromaidan protests that led to the ouster of former President Viktor Yanukovych.
European Commission experts estimate the deal will boost Ukraine's national income by 1.2 billion euros ($1.6 billion) a year.
In Washington, U.S. State Department spokeswoman Marie Harf said Russian interference in Ukraine had failed.
"I think it is noteworthy that exactly what President [Vladimir] Putin was trying to prevent from his interfering in Ukraine has now happened," she said.
Georgia and Moldova, two other former Soviet republics, also signed trade and political accords with the EU in Brussels on June 27.
Russian Deputy Foreign Minister Grigory Karasin said the signing would have "grave consequences" for Ukraine.
White House spokesman Josh Earnest called such threats "unhelpful."
The State Department, meanwhile, cast doubt on a report by the UN High Commissioner for Refugees claiming that 110,000 Ukrainians had fled to Russia so far this year.
Spokeswoman Harf said the UN figures had not been confirmed by the United States.
Harf said it was credible that thousands had fled the conflict, but also noted there is constant human movement along the porous border between Ukraine and Russia.
With reporting by AFP, Reuters, and UNIAN