Ukraine blamed pro-Russian rebels for complicating the situation in the east as skirmishes killed two government soldiers and left seven wounded less than two months into a cease-fire.

Separatists fired on Ukraine troops 30 times during the day Saturday, the Defense Ministry said on Facebook. They were also redeploying and procuring more weapons and military vehicles from Russia, Andriy Lysenko, a Ukrainian military spokesman, said earlier in Kiev.

Even as the truce, negotiated last month in Minsk, Belarus, is disrupted by clashes, it has helped to reduce casualties in a conflict that has claimed the lives of more than 6,000 and devastated Ukraine's economy. The country and Germany, which were among parties that brokered the cease-fire, are calling for fresh talks as the government and rebels accuse each other of violations.

The situation in the conflict area "remains difficult," Lysenko said. "The shelling of towns proves yet again that fighters neglect civilian lives and aim to escalate the conflict."

The U.S. and European Union have imposed sanctions on Russia, which they accuse of stoking violence by aiding the insurgents. While Russia denies such claims, the EU has pledged to prolong the bloc's sanctions in the wake of breaches. The rebels said they are preparing for a new offensive to expand their territory, endangering the six-week-old truce.

"We'll try to push them from here to hell because we're tired of them killing civilians with indiscriminate fire," rebel Alexander Khodakovsky, who commands the 3,500-man Vostok Brigade, said in an interview at his headquarters in Donetsk. The campaign may start in the "foreseeable future," said Khodakovsky, who also heads the security council of the self-proclaimed Donetsk People's Republic.

Ukraine's army, meanwhile, is digging in to defend the key port of Mariupol, which NATO views as a key objective in any rebel bid to create a land bridge from Russia to Crimea, the territory Russia annexed from Ukraine a year ago. The Sea of Azov port city, home to half a million people, is the largest government stronghold between separatist-held territory and the Black Sea peninsula.

"We are constantly working to strengthen Mariupol's line of defense," Zoryan Shkiryak, an adviser to the Interior Ministry, said Thursday in a statement on the government's website. "We are digging antitank ditches, we are building fortifications."