The Ukrainian government says its forces have relaunched an "antiterrorist operation" against pro-Russian separatists in the east after a 10-day truce failed to resolve the crisis.
Speaker Oleksandr Turchynov told parliament on July 1 that "this morning, the active phase of the antiterrorist operation was resumed. Our armed forces are attacking the terrorists' bases and strongholds."
President Petro Poroshenko announced on June 30 that he would not renew the cease-fire and that Ukrainian forces would go on the offensive.
The cease-fire, which was part of his plan to end a pro-Russia insurgency in the east, expired late on June 30. Poroshenko had extended the cease-fire from the initial seven days to 10 days.
A statement tweeted by Ukraine's Foreign Ministry said 27 Ukrainian soldiers had been killed since the cease-fire began on June 20.
A video statement from Poroshenko on his website said "we will attack and we will free our land."
Russian Foreign Minister Sergei Lavrov said Poroshenko's decision not to extend the truce started “a new cycle of bloodshed with consequences unpredictable for the Ukrainian state.”
The Foreign Ministry said Lavrov made the comments during a telephone conversation with U.S. Secretary of State John Kerry.
It said Kerry gave assurance on Washington's desire to find a peaceful resolution to the conflict but "acknowledged differences in the approaches on how to achieve this."
Ukrainian military spokesman Oleksiy Dmytrashkovsky said government forces had begun artillery fire and carried out air strikes.
Dmytrashkovsky said rebels had fired on an SU-25 attack aircraft, damaging it, but that the plane had managed to land safely at its base.
Kyiv said its forces regained control of the Dovzgansky border crossing in Luhansk, on the country's border with Russia, while rebels claimed they took control of the Luhansk airport.
Gun Battles In Donetsk
In the city of Donetsk, reports said the separatists took over the Interior Ministry compound after hours of gun battles.
Separatists in the Donetsk region say four people were killed when a shuttle bus was hit by gunfire in the city of Kramatorsk, without giving further details.
A separatist leader in Donetsk, Miroslav Rudenko, told Russia's Interfax news agency that fighting had broken out in Kramatorsk, the village of Karlivka, and at Donetsk's airport.
Witnesses also told local media that a tank battle was under way in the area of Karlivka, a village northwest of Donetsk.
Poroshenko's decision to call off the cease-fire followed four-way talks with Russian President Vladimir Putin, German Chancellor Angela Merkel, and French President Francois Hollande on June 30 before the deadline expired.
Poroshenko said he was willing to return to a cease-fire "at any moment" if it became clear that all sides were ready to carry out all aspects of his peace plan, including the freeing of hostages and creating effective border controls.
Meanwhile, the European Union decided not to immediately impose new sanctions on Russia, saying the picture on the ground remains “mixed.”
Ambassadors from the 28-nation bloc discussed the issue at a meeting in Brussels on July 1.
However, EU diplomats were quoted as saying the governments decided that "the preparation of sanctions will be intensified."
Sources said the ambassadors will convene again on July 7 to discuss the situation, and that EU experts were working on sanctions targeting specific people or companies.