French Foreign Minister Laurent Fabius said on Wednesday Russia would face more sanctions if pro-Moscow fighters attack Ukraine's government-held port of Mariupol.

"We've told the Russians clearly that if there was a separatist attack in the direction of Mariupol, things would be drastically changed, including in terms of sanctions," Fabius told France Info radio.

The question of sanctions would be asked again at the European level, the minister said.

Asked whether France would send servicemen to Kiev, Fabius said, "We advocate de-escalation."

Fabius met his German, Russian and Ukrainian counterparts, under the so-called Normandy format, on Tuesday to discuss ways to implement the Minsk peace deal and halt fighting in Ukraine's eastern region.

The top diplomats also asked for a reinforcement of the Organization for Security and Co-operation (OSCE) monitoring mission in Ukraine.

Also on Tuesday, more than a week after the latest Minsk ceasefire agreement, separatist insurgents said they had begun pulling back heavy weapons from the front line in eastern Ukraine.

Ukrainian military sources said the military would start withdrawing heavy arms from the front line no earlier than two days after a complete ceasefire.

The Minsk ceasefire deal was brokered by Paris and Berlin on Feb. 12 in the capital of Belarus. It envisaged both sides withdrawing heavy weapons 25-70 km from the front line to create a buffer zone.

Under the agreement, both sides were meant to start withdrawing heavy weaponry from the battle area no later than two days after the start of a truce which came into force on Feb. 15.