An already shaky cease-fire teeters on the brink of collapse after clashes in eastern Ukraine. As each side blames the other, Ukraine's president has said there is a "colossal threat" of large-scale fighting.
The worst flare-up of violence between Ukrainian troops and pro-Russian separatists in months has led to the deaths of at least 24 people. At least five civilians, 14 separatist fighters and five Ukrainian soldiers were killed in fighting in eastern Ukraine, according to media reports.
Battles took place near the town of Maryinka, which Kyiv said separatists had tried to capture on Wednesday. Lower-level fighting in the region has continued despite a February cease-fire agreement brokered by Germany and France, but recent clashes have included the use of heavy weapons on both sides.
Observers from the Organization for Security and Cooperation in Europe on Thursday reported that they witnessed heavy weapons firing from separatist-controlled regions of eastern Ukraine.
A Ukrainian military spokesman told Reuters news agency on Thursday that the situation near Maryinka remained "tense but stable."
"On three occasions the [separatist] fighters shelled our positions during the night," he said. "At the moment there is an operation going on to find sabotage and diversionary groups."
Ukrainian President Petro Poroshenko said Thursday there was a "colossal threat" of large-scale military operations in eastern Ukraine. In his annual address to parliament, he added that there were estimated to be more than 9,000 Russian troops on Ukrainian territory and that Ukraine's army needs to be ready for a "full-scale invasion" along the country's entire border with Russia.
Both Moscow and Kyiv have accused each other of intentionally trying to scrap the peace deal.
Russia has denied sending military troops to Ukraine and on Thursday accused Kyiv of not keeping promises it made to uphold the cease-fire.
"The February Minsk [cease-fire] agreements are constantly under threat because of the actions of the Kyiv authorities, trying to walk away from their obligations to foster direct dialogue with Donbass," Russian Foreign Minister Sergei Lavrov said, referring to the rebel-held region in eastern Ukraine.
The US State Department countered that Russia had not done its part to persuade separatists in the region to put down their weapons.
Violence gets G7 world leaders' attention
Russia, whose economy is suffering under economic sanctions placed on the country by the United States and the European Union, said Ukraine was upping violence ahead of a G7 meeting of world leaders in Germany this weekend.
"The Ukrainian side has taken steps to aggravate tensions many times in the past in the run up to some major international events. This used to happen and we are seriously concerned now over the most recent manifestation of such activity," Kremlin spokesman Dmitry Peskov told journalists.
A German government spokesperson questioned whether the world leaders' meeting was connected to the intensified fighting, saying only that "heavy violations" of the cease-fire were "worrying."
sms/msh (AFP, Reuters, AP, dpa)