Russian forces are stepping up attacks in eastern Ukraine in a bid to take full control of the strategic city of Mariupol. The objective may be to gain leverage in ceasefire negotiations.

Russia's defense ministry said on Thursday its military used cruise missiles to destroy fuel depots in eastern Ukraine. It said Russian forces placed more areas in the east under their control.

There is no letup in the humanitarian crisis in Mariupol. Some military analysts say Russian troops could take control of the whole city in a matter of days.

Moscow promised to scale back its military operations around Kyiv and Chernihiv after ceasefire talks in Istanbul on Tuesday.

But US defense officials say some of the troops may only pull back to Belarus for reorganization and replenishment.

Britain's defense ministry says Russian forces continue to hold positions to the east and west of Kyiv. It says heavy fighting will likely take place in the suburbs of the capital within days.

Ukrainian officials say ceasefire negotiations will resume online on Friday. Russia may respond to Ukraine's proposal for a new framework to ensure the country's security without becoming a NATO member.

Turkey's foreign minister said Thursday his country may mediate talks between the Russian and Ukrainian foreign ministers within the next week or two.

Meanwhile, US and British officials say President Vladimir Putin's aides appear to be too afraid to tell their leader the truth about how Russian forces are faring in the face of fierce Ukrainian resistance.