Ukraine's border guards service said a serviceman was killed and eight were wounded when a post on the border with Russia came under heavy mortar attack.

In a statement, the service said the attack took place before dawn Wednesday, July 2, at the Novoazovsk post in the southeastern part of the Donetsk region.

A 10-day unilateral cease-fire by the Ukrainian side expired late Monday after pro-Russian armed groups rejected calls to lay down their weapons.

Border posts have become key strategic objects, as Ukraine claims the armed men are receiving support and reinforcements from Russia.

Ukraine says it retook control of one border post this week. The guards service said Wednesday "the insurgents had mined the post with explosives."

The government forces pressed on with a military drive on Wednesday as Ukraine, Russia, Germany and France prepared a meeting of foreign ministers to try to bring the crisis in Ukraine's east under control.

"The armed forces and the National Guard are continuing the offensive on terrorists and criminals. The actions of our military are effective and are having results," parliament speaker Oleksander Turchynov said, according to Reuters.

The move won backing from the United States, but drew criticism from Russian President Vladimir Putin who said the newly-elected Ukrainian leader had veered off the road to peace.