Ukrainian forces have regained control of the strategically important port city of Mariupol, says the interior ministry. Meanwhile, a number of Russian military vehicles have reportedly crossed into Ukrainian territory.
Ukrainian Interior Minister Arsen Avakov wrote on Friday that the country's armed forces had recaptured Mariupol. Clashes between Ukraine's National Guard and separatist fighters erupted there just after dawn and lasted for several hours, according to a statement he posted on Facebook.
"At 10:34 a.m. (0734 UTC) the Ukrainian flag was raised over City Hall in Mariupol," Interior Minister Avakov wrote.
"The area where the operation is being conducted in central Mariupol has been sealed off," he wrote.
It was not immediately clear how many fighters had been injured in the clashes.
Ukrainian forces have been fighting to uproot pro-Russian separatists in eastern Ukraine, where rebel leaders have claimed independence from the pro-EU government in Kyiv. Newly elected Ukrainian President Petro Poroshenko vowed after May 25 election to end fighting by the weekend and launch peace talks with militants who have "no blood on their hands."
Mariupol has strategic importance due to its location close to the Russian border and its role as a major steel exporter. The southeastern port city lies on the Sea of Azov whose waters are skirted by Ukraine, Russia and Crimea.
Russian troops' whereabouts unclear
The Ukrainian military had also retaken a 120-kilometer (75-mile) stretch of its border with Russia by Friday morning, according to Reuters news agency, citing the Ukrainian minister. The report did not specify the border segment.
Sightings of Russian troops in Ukrainian territory emerged late Thursday. According to Avakov, Ukrainian forces had destroyed part of a convoy near the town of Snizhnye.
Meanwhile, Ukrainian President Petro Poroshenko and his Russian counterpart, Vladimir Putin, used a telephone conversation on Thursday to discuss the ongoing crisis in eastern Ukraine, where pro-Russia separatists recently seized control of several cities and towns.
"The president of Ukraine informed Vladimir Putin about his plan to resolve (the problems) in the southeast of Ukraine," the Russian president's spokesman, Dimitry Peskov, was quoted as saying by a number of Russian agencies.
No talks before June 16 deadline
As Kyiv continued its battle to regain ground in the rebel-held cities in eastern Ukraine on Friday, it also mulled over a solution to an impending gas crisis. Russia has threatened to cut off supplies to Ukraine if it fails to pay off another $1.95 billion (1.44 billion euros) of its gas debt by Monday.
EU Energy Commissioner Günther Oettinger expressed hope that talks could continue on Saturday.
"We agreed that both delegations talk to their respective presidents and prime ministers and that happened yesterday," Oettinger told reporters ahead of a meeting with EU energy ministers. "I am expecting that we continue tomorrow, on Saturday."
However, reports emerged on Friday that suggested Russia had different intentions. According to Russian energy ministry commission spokesperson Olga Golant, Russia had not been "planning any meetings so far" with its Ukrainian counterparts.
kms/ipj (AFP, Reuters, dpa)