Kiev, Sep 15 (IANS): Six civilians were killed during renewed intense fighting between government troops and independence-seeking insurgents in Donetsk, the main rebel-held city in eastern Ukraine, municipal authorities said Monday.

According to the press service of the Donetsk municipal council, at least 15 other people were injured in the shelling, which was concentrated near the government-controlled airport, Xinhua reported.

Shells also hit a natural gas pipeline and damaged several apartment buildings in Donetsk.

Besides, fighting also occurred in the outskirts of the city of Lugansk, another rebel stronghold, but there were no reports of casualties there.

Andrei Lysenko, spokesman for Ukraine's National Security and Defence Council (NSDC), said there were deaths and injuries among government troops during the confrontation with insurgents, but he did not elaborate.

The renewed fighting raised fears that a ceasefire for allowing a return of relative calm in eastern regions is on the verge of collapse.

The truce between government troops and insurgents started Sep 5 after representatives of Ukraine's government and insurgent leadership inked a ceasefire deal to pave the way for a solution to the Ukraine crisis.