Trump informed Palestinian president Mahmud Abbas by phone of his intention to move the embassy from Tel Aviv, Abbas's office said on Tuesday.
In an open letter to the American president, the Moroccan king expressed his "deep personal concern" and "the great concern felt by Arab and Muslim states and peoples" over moves to recognise the city as Israel's capital and transfer the US embassy there.
The monarch was writing as head of the 57-member Organisation of Islamic Co-operation's Al-Quds Committee, which lobbies on issues related to the city, holy to three of the world's major religions.
"The current step is likely to negatively impact the prospects of a just and comprehensive solution to the Palestinian-Israeli conflict," the letter said.
The king urged Trump to avoid anything that could "exacerbate feelings of frustration and disappointment, which are the basis of extremism and terrorism".
Trump is due to speak Wednesday on the status of Jerusalem, according to the White House.