Nato chief Jens Stoltenberg yesterday urged Russia to use its influence with pro-Moscow rebels in eastern Ukraine to halt what he called the worst upsurge in fighting in a long time.

"We call on Russia to use its considerable influence with the rebels to bring the violence to an end," Stoltenberg told reporters in Brussels.

"In Ukraine, we see the most serious spike in violence in a long time," he added, citing more than 5,600 ceasefire violations in the past week.

There have been periodic surges in the fighting in eastern Ukraine but the latest clashes come just after US President Donald Trump took office promising to try to improve ties with Russia, including a possible relaxation of the sanctions.

Trump talked with Russian President Vladimir Putin at the weekend in a call the White House described as a "significantstart" to improving ties.

The death toll rose to 19 yesterday as Ukraine government forces and the rebels exchanged mortar and rocket fire for a fourth day around the flashpoint eastern town of Avdiivka, just north of the rebels' de facto capital Donetsk.

Kiev said three of its soldiers died overnight while the rebels said four civilians had been killed.