US, Britain mulling 'extra sanctions' against Russia: Kerry

London: The US and Britain are considering deepening sanctions against Russia due to its "craven behaviour" in Ukraine, Secretary of State John Kerry said before talks with British counterpart Philip Hammond in London on Saturday.

"We are talking about additional sanctions, additional efforts," Kerry told reporters.

"We`re not going to sit there and be part of this kind of extraordinarily craven behaviour at the expense of the sovereignty and integrity of a nation."

The pair met following a bloody few days in the Ukraine`s east as Russian separatists and Ukrainian forces fought fiercely despite the announcement of a new ceasefire.

It was meant have gone into force on Sunday, but Ukraine and the US have pointed to repeated violations, including the seizure of the strategic town Debaltseve by rebels they claim Moscow is backing.

Top US diplomat Kerry said he was "confident that during the course of the next days that people are determined to make it clear we`re not going to play this game."

Ukraine lost 179 troops in the one-month battle for Debaltseve, Yuri Biryukov, an advisor to Ukraine`s president said on his Facebook page Saturday.