Update as of 04:32am EDT: A Reuters witness heard prolonged shelling in an area north of Donetsk, eastern Ukraine's largest city, and saw plumes of black smoke filling the sky on Sunday morning, in a further test for a cease-fire that is barely 40 hours old.

The shelling came from near the airport, which has been in the hands of Ukrainian government forces though pro-Russian rebels control the city. Rebels told Reuters the airport itself was now empty and that the fighting was centered on a nearby military compound.

"Listen to the sound of the cease-fire," joked one armed rebel. "There's a proper battle going on there."

Overnight the port of Mariupol on the Sea of Azov, to the south of Donetsk, also saw a serious violation of the cease-fire when government forces came under artillery fire. There was no word on casualties.

(Reporting by Gabriela Baczynska, writing by Gareth Jones)

Original story below

Explosions have reportedly been heard near the Ukrainian cities of Mariupol, Luhansk and Donetsk, multiple sources said late Saturday. The apparent attacks elevate suspicions that Russian-backed rebels have broken a day-old cease-fire agreement with Ukraine.

Witnesses in the port city of Mariupol told the Associated Press by phone that heavy explosions were heard in the city’s eastern outskirts, where Ukrainian troops are holding a defensive line against the separatists. Col. Andriy Lysenko, a representative of Ukraine’s national security council, told reporters that rebels had fired at Ukrainian forces on 10 occasions Friday night, just hours after the cease-fire pact took effect, AP said.

The cease-fire agreement came Friday afternoon after leaders of the Ukrainian government, the Russian government, rebel groups and the Organization for Security and Cooperation in Europe met for peace talks in Minsk, Belarus. More than 2,600 people have died in the conflict that began in April, according to the United Nations.

Earlier Saturday, Russian President Vladimir Putin and Ukrainian President Petro Poroshenko said the cease-fire was “largely holding,” BBC News reported. The men said they had spoken by phone to discuss steps to make the cease-fire last.

“Both leaders expressed satisfaction with the fact that the parties to the conflict are generally complying with the ceasefire,” the Putin administration said in a statement posted at 6:40 p.m. Moscow time (10:40 a.m. EDT). Putin and Poroshenko “agreed to continue their dialogue.”

Yet, hours later, BBC reporter Fergal Keane had a series of tweets in Mariupol along the following line:



Keane said cease-fire violations also had been reported elsewhere, but that the agreement’s overall status would not be clear until Sunday morning:



Russian separatists also accused Ukrainian forces of attacks outside Donetsk, a southeastern city near Mariupol and the largest area controlled by separatists, AP said. Alexander Zakharchenko, a top rebel leader, told the Russian news agency RIA Novosti that Ukrainian troops had violated the cease-fire with two rounds of shelling there.

North of Donetsk, the International Committee of the Red Cross reported shelling near the heavily embattled city of Luhansk via Twitter:



Meanwhile, back in Mariupol at 1:55 a.m. local time (6:55 p.m. EDT), Keane tweeted: