Massive Blasts and Gunfire Rock Separatist Stronghold in Ukraine

Several casualties have been reported after booming explosions from shelling rocked the city of Donetsk on Sunday. A thick plume of black smoke was seen rising over the eastern separatist stronghold, authorities said.

Heavy fighting flared around the airport, which pro-Russian and Ukrainian forces have been battling over for several months. The Ukrainian military said it fended off attacks on the airport Saturday, according to the Guardian.

A local market and residential blocks in the area were hit by mortars and Grad missiles during the latest clashes. At least six civilians were killed in the crossfire, according to reports from journalists on the ground in the area.

A Donetsk city council statement released Sunday said that the situation in the city is now "critical" amid the relentless shelling. No official casualty figures were given.

War in Peace: Divided East Ukraine Braces As Ceasefire Crumbles. Read more here.

The videos and descriptions of renewed fighting in the country's east come a little more than a week after the Ukraine entered into a long-term conditional ceasefire with pro-Russian separatists in the region. But reports that the fragile truce was already crumbling have come throughout the week, and heavy artillery and gunfire sounded on the eastern outskirts of Mariupol and Donetsk.

In the past few days, both sides have blamed each other for violating the peace agreement signed September 5 in Minsk, Belarus. The deal set the parameters for a halt to the hostilities, including a prisoner swap, the withdrawal of heavy weaponry, and permission for humanitarian aid to flow back into the war-ravaged area.

Despite the alleged violations, an end to the ceasefire has not yet been officially declared.

Speaking at a conference in Kiev over the weekend, Ukrainian President Petro Poroshenko, said that there would be "no military solution" to the conflict.

But, in a sign of a growing divide between Ukraine's political leaders, Prime Minister Arseniy Yatsenyuk said that Ukraine is "in a state of war with Russia."

"He [Putin] cannot cope with the idea that Ukraine would be a part of a big EU family. He wants to restore the Soviet Union," Yatsenyuk said. "His goal is to take the entire Ukraine."

Political tensions are mounting in the capital following the opening of campaigning for a parliamentary election scheduled for October 26. Observers form the Organization for Security and Cooperation in Europe (OSCE), which is monitoring the truce, noted that the agreement had been "generally" respected.

The OSCE also reported that it had overseen the exchange of 68 prisoners of war in Avdeevka, a town roughly 12 miles north of Donetsk. Ukrainian forces swapped 31 prisoners and the rebels exchanged 37.

Foreign governments, however, remain skeptical of the accord.

"With respect to the ceasefire agreement, obviously we are hopeful but based on past experience also skeptical that in fact the separatists will follow through and the Russians will stop violating Ukraine's sovereignty and territorial integrity. So it has to be tested," President Obama told reporters on the day the ceasefire was announced.

The UN estimates that some 3,000 people have been killed since mid-April as a result of ongoing fighting between the Ukraine army and Russian-backed rebels.

Ukraine Reaches Ceasefire Agreement with Pro-Russia Forces. Read more here.

VICE News reporter Harriet Salem contributed to this report.

Follow Liz Fields on Twitter: @lianzifields