There has been no response from Russia or separatist leaders in Ukraine to Ukrainian President Petro Poroshenko's request for a new round of talks on Saturday.
Poroshenko said he suggested a time and place for the talks during a phone call with European Union foreign policy chief Catherine Ashton. He said he is waiting for the other side to confirm.
The EU and United States have threatened Russia with more sanctions if Moscow and the pro-Russian fighters in eastern Ukraine do not take steps to de-escalate the crisis.
The fighting has picked up since Ukraine ended a unilateral cease-fire earlier this week.
Ukrainian forces claim they retook a village Friday in the rebel-held region of Slovyansk, one of the hot spots of the fighting.
Numerous phone calls
Earlier Friday, Poroshenko, German Chancellor Angela Merkel and French President Francois Hollande discussed the situation in eastern Ukraine in a three-way phone call.
Merkel's office said they agreed that a mutual cease-fire is a prerequisite to stabilize the situation and that Kyiv and Moscow must work together to secure the Ukrainian-Russian border. They also called on Russia to "use its influence over the separatists."
Merkel discussed the Ukraine crisis with President Barack Obama in a telephone call Thursday.
The White House said in a statement that the two leaders "stressed that Russia must take immediate steps to de-escalate" the conflict and agreed that the U.S. and Europe "should take further coordinated measures to impose costs on Russia if it does not take steps toward de-escalation in short order."
On Wednesday, the foreign ministers of Ukraine, Russia, France and Germany met in Berlin and said talks aimed at resuming a cease-fire between the Ukrainian military and pro-Russian rebels should begin no later than Saturday.
Last month, separatist leaders met with Ukrainian ex-president Leonid Kuchma as Kyiv's representative. Moscow's ambassador to Kyiv and members of the Organization for Security and Cooperation in Europe (OSCE) also attended the talks in the eastern Ukrainian city of Donetsk.
President Poroshenko declared a unilateral, week-long cease-fire June 20 and then extended it by three days. Citing lack of cooperation from rebels, he refused a second extension and ordered the resumption of military operations on Tuesday.
The Ukrainian president told Vice President Joe Biden in a phone conversation Thursday he was ready to return to a cease-fire as soon as it can be confirmed that both sides are observing it. He also said a cease-fire was contingent on all hostages being released and control over the Ukrainian-Russian border being established, with monitoring by the OSCE.
Fighting continues in eastern Ukraine, with the press center of Kyiv's "anti-terrorist operation" reporting that nine Ukrainian servicemen had been killed and 13 wounded in battles with separatist forces on Friday as of 2 p.m. local time.
Also Friday, Ukraine's Foreign Ministry sent a note of protest to Moscow over what it called "regular gross violations of Ukrainian airspace" by Russia. It detailed what it said were several separate incidents on Thursday in which Russian military helicopters flew over Ukrainian territory
The secretary of Ukraine's National Security and Defense Council, Andriy Parubiy, said Friday that if Russian aircraft violate Ukrainian airspace again, they will be shot down.
Some information for this story was provided by Reuters and AFP.
A military vehicle bearing a Ukrainian flag at a checkpoint near Slaviansk in eastern Ukraine, July 3, 2014.
A woman holds a sign a protest against the crisis in eastern Ukraine orgainsed by the Russian communist party in Moscow ,July 3, 2014.
Volunteers from the Donbass battalion and Maidan self-defense group stand guard with official security guards outside the Ukrainian parliament in Kyiv, July 3, 2014.
Relatives grieve after traffic police officers were attacked by unknown assailants in the eastern Ukrainian city of Donetsk, July 3, 2014.
Pro-Russian fighters stand patrol near Luhansk, eastern Ukraine, July 2, 2014.
Workers remove concrete slabs from a school damaged through attacks, in Luhansk, eastern Ukraine, July 2, 2014.
People carry their belongings as they walk to cross the border into Russia at the Ukrainian-Russian border checkpoint in Severniy, Luhansk region, eastern Ukraine, July 2, 2014.
Municipal workers remove tires as they dismantle barricades set up during the protests that toppled Moscow-backed president Viktor Yanukovych in central Kyiv, July 1, 2014.
A man and his daughter walk to a pumping station to get water in the eastern Ukrainian city of Slovyansk, July 1, 2014.
An armed pro-Russian separatist stands guard at a check point in the Ukrainian eastern city of Slovyansk, July 1, 2014.
A woman and children walk past a damaged street market in the Ukrainian eastern city of Slovyansk, July 1, 2014.
People collect water at a pumping station in the Ukrainian eastern city of Slovyansk, July 1, 2014.
Valery, who gave only his first name, carries his injured cat in front of his damaged house after shelling, in the city of Slovyansk, June 30, 2014.
A man looks out of a window of his apartment, which was damaged by shelling, in Slovyansk in eastern Ukraine, June 30, 2014.