Sergei Lavrov, 8/17/15
Russian Foreign Minister Sergei Lavrov speaks during a news conference after meeting with Iranian counterpart Mohammad Javad Zarif in Moscow, Monday, Aug. 17, 2015. Lavrov accused Ukraine of preparing a new offensive against pro-Moscow separatists. Reuters/Maxim Zmeyev

Russian Foreign Minister Sergei Lavrov said Monday that Ukraine's military was preparing a new offensive against Russian-backed rebels in contested eastern Ukraine, the Russian news agency Tass reports. Lavrov's contention, which follows a week of intense confrontation that left more than 15 dead and dozens wounded, counters similar claims by Kiev that pro-Russian rebels were preparing their own attacks to take the strategic coastal town of Mariupol.

"We are worried by the developments in recent days which strongly recall preparation for more military actions," said Lavrov at a news conference in Moscow. "It was like that in August last year when Ukrainian soldiers received the order to attack. It was like that in January of this year. One shouldn't be experimenting and trying one's luck, one should simply fulfill what was agreed in Minsk."

Kiev, however, says sustained attacks near the Ukrainian-held city of Mariupol, an economically important port for the Donbas region on the Sea of Azov coast, suggest that rebels are also making a sustained push west. From Sunday evening into Monday morning, the Ukrainians said their forces were attacked more than 140 times in positions around Mariupol.

Ukraine war, Donetsk
A man cries amid the debris of his home, which according to locals was hit by recent shelling, in Donetsk, Ukraine, Monday, Aug. 17, 2015. Reuters/Alexander Ermochenko

While the Minsk II ceasefire has helped ease fighting since it was signed in February, deadly clashes over the last week have threatened to see full-scale fighting return to the region. In skirmishes near Donetsk last week, seven Ukrainian soldiers were killed and more than 40 wounded. The day was one of the deadliest since the ceasefire was agreed. Ukrainian forces said after that they would reintroduce banned heavy weapons into their armory if rebel troops continued to attack with tanks and heavy artillery.

German Foreign Minister Frank-Walter Steinmeier called for calm and asked that both parties, along with the Organization for Security and Co-operation in Europe, the independent group charged with monitoring the conflict, come back to the negotiating table and find a diplomatic solution.

Since fighting began in April 2014, more than 7,000 civilians and military personnel have lost their lives, and 1.5 million Ukrainians have become displaced.