The top House Democrat with oversight of foreign affairs warned Thursday that the Trump administration's move to recognize Morocco’s claims to contested territory in the Western Sahara threatens efforts at international diplomacy to solve long-standing conflicts.

President Trump on Thursday announced a breakthrough of diplomatic relations between Israel and Morocco that came with the U.S. recognizing Rabat’s sovereignty over annexed territory in Western Sahara, of which its final status has been stalled since 1991 under an international peace process.

Rep. Eliot Engel (D-N.Y.), the outgoing chair of the House Foreign Affairs Committee, welcomed the move forward in open relations between Jerusalem and Rabat, but warned against “casting aside legitimate multilateral avenues of conflict resolution."

“I welcome the news that Israel and Morocco have normalized relations,” Engel said in a statement.

“At the same time, I am concerned this announcement upends a credible, internationally supported UN process to address the territorial dispute over Western Sahara, which successive administrations of both parties have supported,” he added. 

Morocco annexed the territory of Western Sahara in 1979 in a move that was not recognized by the international community and failed to bring an end to ongoing violence in the region between the Polisario independence movement on behalf of indigenous Sahrawi people. The status over the Western Sahara also contributes to tensions between Morocco and neighboring Algeria, which backs the Polisario Front and is host to hundreds of thousands of Sahrawi refugees.

A 1991 cease-fire, negotiated within the United Nations, was an attempt to establish a referendum on the final status of the territory. Last month, a flareup of violence in the region raised the risk of a collapse of the cease-fire, although Moroccan officials denied that it was involved in clashes with the Polisario Front.

Engel further criticized Trump’s move as emboldening countries like China and Russia to take territory by force. The U.S. has opposed Russia’s 2014 annexation of Crimea and ejected Moscow from what was then the Group of Eight intergovernmental organization, now the Group of Seven.

“Casting aside legitimate multilateral avenues of conflict resolution only empowers countries like Russia and China to continue trampling on international rules and norms and rewards those who violate borders and the rights of free peoples,” Engel continued.

“I call on all parties in North Africa to exercise restraint, refrain from violence and continue to work toward a just and lasting solution.”

The House chairman also called for more efforts to bring Israelis and Palestinians back to the negotiating table, which the Trump administration says reflects outdated thinking amid its push to open diplomatic ties with Arab- and Muslim-majority nations. 

Still, the United Arab Emirates agreed to open diplomatic ties with Israel in exchange for Jerusalem suspending plans to annex parts of the West Bank, a move supporters of an independent Palestinian state said would have damaged efforts at achieving a two-state solution. 

“As four more Arab countries have now shown that the future of the region is found in a path toward peace with Israel, I urge Israelis and Palestinians to return to the negotiating table and recommit to a sustainable, peaceful two state-solution,” Engel said.