Ukrainian government forces and separatist rebels both claimed to have made gains Tuesday ahead of a planned peace summit involving Western leaders.

Ukrainian President Petro Poroshenko told Parliament that Russian-backed rebels launched an artillery strike on the town of Kramatorsk, which is more than 30 miles away from the front line. Poroshenko said the first round of rocket fire hit the headquarters of the Ukrainian command in eastern Ukraine and the second landed in a residential area.

The government-controlled Donetsk administration said seven civilians were killed and 26 civilians and 32 servicemen were wounded by the rocket barrage. Photos on the local Donetskiye Novosti website showed an artillery shell stuck in the ground next to a residential building and two bodies lying nearby.

Kramatorsk was the site of major fighting until July when pro-Russian separatists retreated from it.

Local website Donetskiye Novosti posted photos from the scene, showing an artillery shell stuck in the ground next to a residential building and two bodies lying nearby.

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The volunteer Azov battalion, loyal to Kiev, said on social media on Tuesday that it captured several villages northeast of the strategic port of Mariupol, pushing the rebels closer to the border with Russia. However, rebel military spokesman Eduard Basurin said in a televised news conference that the rebels have not retreated.

The Azov said rebels shelled the village of Kominternove, east of Mariupol, causing unspecified civilian casualties. An Associated Press reporter at a government check-point between there and government-controlled Mariupol was told of ongoing fighting several miles away. Two ambulances and four pick-up trucks carrying Ukrainian troops were seen coming from the direction of Kominternove toward Mariupol.

Rebels reported advances, too. Basurin said late Monday that they have surrounded the railway hub of Debaltseve, the focus of fierce fighting in the past weeks, cutting it off from a major highway. A video posted online by a rebel-sympathizing website showed the separatists moving along the highway while the bloodied bodies of Ukrainian soldiers lay on the side of the road.

At least seven Ukrainian troops were killed overnight in the east, Ukrainian military spokesman Anatoliy Matyukhin said on Tuesday. In the rebel stronghold of Donetsk, which comes under constant shelling, two civilians were killed and 12 injured.

The fierce fighting and a mounting death toll comes amid renewed efforts to work out a peaceful solution in a conflict that has displaced at least 1 million people and left the powerhouse of the Ukrainian economy in ruins.

Representatives of Ukraine, Russia, rebels and the Organization for Security and Cooperation in Europe are meeting for long-anticipated talks later on Tuesday to lay the groundwork for a meeting on Wednesday between the leaders of Russia, Ukraine, Germany and France.

The Kremlin on Tuesday warned the West ahead of the talks against sending weapons to Ukraine or putting pressure on Russia.

Russian President Vladimir Putin's spokesman, Dmitry Peskov, told the Russian News Service radio station on Tuesday that any talk about imposing new sanctions on Russia or arming the Ukraine government would destabilize the situation in Ukraine.

The talks in Minsk on Tuesday were tentatively scheduled for 6 p.m. local time, the Belarusian foreign ministry said.

Poland Defense Minister Tomasz Siemoniak said Tuesday that his country will not send lethal weapons to Ukraine but said there was little optimism in the West about the outcome of peace negotiations given Russia's "low credibility." He said on Polish Radio 1 that the first step should be a ceasefire, "and then we can talk."

"I want it to be clear. It is out of the question to send heavy weaponry to Ukraine, or Grom missiles, tanks or similar weaponry. Poland did not have and has no such plans," Siemoniak said.

In Washington on Monday, President Barack Obama and German Chancellor Angela Merkel rallied behind efforts to reach a long-shot diplomatic resolution to the conflict, but they offered no clear path for how the West would proceed if talks this week fail. Merkel staunchly opposed arming Ukraine's beleaguered military while Obama dangled the prospect that the U.S. could for the first time send weapons to Ukraine.

The Associated Press contributed to this report.