Russia on Friday condemned US President Donald Trump's decision to recognise Morocco's sovereignty over Western Sahara, saying it contravened international law.

Deputy Foreign Minister Mikhail Bogdanov called the US decision "unilateral", Russian news agencies reported, adding that "there are relevant resolutions, there is the United Nations Mission for the Referendum in Western Sahara."

"This is a violation of international law," Bogdanov said.

Western Sahara is a disputed and divided former Spanish colony, mostly under Morocco's control, where tensions with the pro-independence Polisario Front have simmered since the 1970s.

The Algerian-backed movement holds a fifth of Western Sahara and has campaigned for a vote on self-determination through decades of war and deadlock.

With barely a month left in office, Trump fulfilled a decades-old goal of Morocco's by backing its sovereignty in Western Sahara. The move was part of the outgoing US leader's diplomatic push to bring Israel and Arab states together.

He announced on Thursday that Morocco was now the fourth Arab state this year to recognise Israel.

Russia's Bogdanov said Moscow saluted better ties between Morocco and Israel.

"That Arab countries are building bridges with Israel is positive, we can only support this," he said.

But, he added, this should not be done "at the expense of the interests of the Palestinian people".