Algeria on Saturday rejected a decision by outgoing U.S. President Donald Trump to recognise Moroccan sovereignty over Western Sahara, saying the step would undermine efforts to end the decades-long conflict over the desert territory.

Trump’s administration said it was recognising Moroccan claims to Western Sahara as part of a deal under which Morocco agreed to normalise its relations with Israel.

In Algiers, the Foreign Ministry said the U.S. decision “has no legal effect because it contradicts U.N. resolutions, especially U.N. Security Council resolutions on Western Sahara”.

“The proclamation would undermine the de-escalation efforts made at all levels in order to pave the way for launching a real political process,” the ministry said in a statement.

The U.S.-Morocco deal comes at a key moment in the long-frozen conflict in Western Sahara between Morocco and the Algeria-backed Polisario Front independence movement, which erupted again last month after three decades of truce.

The United Nations and other Western states are not expected to change their long-standing position calling for a referendum to resolve the dispute. The United Nations said its stance was unchanged.