The United States on Sunday started the "process of establishing" a consulate in contested Western Sahara, after Washington recognised Morocco's sovereignty there in exchange for Rabat normalising ties with Israel.

US ambassador David Fischer visited the port of Dakhla, 1,440 kilometres (895 miles) southwest of Rabat in the far south of Moroccan-controlled Western Sahara, to mark the start of work on a diplomatic office.

"It is such an honour for me to visit this stunningly beautiful and critically important region of Morocco, and to begin the process of establishing a US diplomatic presence here," Fischer said, according to the US embassy.

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.

Last year, Morocco joined the United Arab Emirates, Bahrain and Sudan in agreeing to normalise ties with Israel under US-brokered deals.

In return, US President Donald Trump fulfilled a decades-old Moroccan goal by backing its contested sovereignty over the barren but phosphate-rich region, which lies next to key Atlantic fishing zones.

Foreign Minister Nasser Bourita said Sunday that "Morocco feels stronger in its legitimate fight for its territorial integrity... with the support of its friends."

The Algerian-backed Polisario Front fought a war for independence from 1975 to 1991 and controls about one fifth of the desert territory.

UN peacekeepers in Western Sahara are mandated to organise a referendum on self-determination for the region, and despite Washington's move, the UN insists its position is "unchanged".

In November, the Polisario announced it regarded a 1991 ceasefire as null and void, after Morocco sent troops into a UN-patrolled buffer zone to reopen a key road.

Fischer, who called the visit Sunday "another historic milestone in more than 200 years of friendship" between Morocco and the US, was accompanied by Assistant Secretary of State for Near Eastern Affairs David Schenker.

In December, the US State Department opened a "virtual" diplomatic post in Western Sahara, ahead of finding "an appropriate site" to build a consulate.

The building is expected to be ready in coming months, Fischer added.

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