Turkish President Recep Tayyip Erdogan threatened to cut ties with Israel should U.S. President Donald Trump recognise Jerusalem as its capital, portending the backlash the move would likely cause in Muslim-majority nations.

“Mr Trump, Jerusalem is a red line for Muslims,” Erdogan said in a speech at parliament in Ankara on Tuesday. “This could lead us to break off our diplomatic relations with Israel.”

Trump had been expected to signal his intention on Monday, when he was due to decide whether to renew his signature on a waiver to keep the U.S. embassy in Tel Aviv. But no action was made public, and a White House spokesman said an announcement would be made in the coming days. The decision is fraught with religious and political implications with Jerusalem, home to some of the holiest ancient sites in Judaism, Christianity and Islam, also claimed by Palestinians as the capital of a future state.

Relations between Turkey and Israel, whose alliance was once a bulwark of the U.S.’s Middle East security posture, have deteriorated as Erdogan moved to redefine his country as a Muslim power and became a fierce critic of Israeli policies in the region. The two countries broke off ties after 2010, when Israeli soldiers raided a Turkish ship trying to break the embargo on the Gaza Strip. Nine Turks were killed on board and a 10th died later. The countries re-established formal diplomatic relations last year.