WASHINGTON — President Trump pressed Saudi Arabia on Wednesday to fully end its blockade of food, water, medicine and fuel into Yemen, a rare humanitarian rebuke to the Middle East ally that he has firmly embraced since taking office.

Saudi Arabia joined Yemen’s civil war, which pit the country’s leaders against Houthi rebels, in 2015. In November, the Saudis intensified a blockade on Yemen, stopping the entry of goods and other basic necessities, and heightening warnings of a humanitarian crisis from international aid groups.

In a brief but blunt statement, Mr. Trump called on the Saudi government to “completely allow food, fuel, water and medicine to reach the Yemeni people who desperately need it.” Mr. Trump added that lifting the blockade “must be done for humanitarian reasons immediately.”

The president’s pointed request to the Saudi monarchy came on the same day that his recognition of Jerusalem as the capital of Israel sparked anger among Saudi leaders, including King Salman, who condemned Mr. Trump’s announcement.

Mr. Trump has emphasized cooperation, not conflict, with Riyadh since becoming president. He has hailed his close relationship with the Saudis and described it as a key part of efforts to combat Islamic extremists.

Even so, Saudi’s ongoing fighting in Yemen has the potential to strain the friendship between the kingdom and the United States, especially in the wake of the blockade, which humanitarian groups described as increasingly dire for Yemen’s civilian population.

Last month, a missile fired from Yemen stuck near the Saudi capital’s airport. Afterward, the kingdom tightened an earlier blockade, closing all of Yemen’s seaports and airports. Those restrictions since have been slightly loosened, but aid groups still say that not enough food or fuel is getting in to prevent further deterioration in the humanitarian situation. The United Nations Security Council on Tuesday said Yemen “stands on the brink of a catastrophic famine.”

American politicians, including Republicans, have urged Mr. Trump to use his leverage with the Saudis to help civilians dying of starvation and lack of medicine in Yemen.

Senator Todd Young, Republican of Indiana, has called on the president and others to clear the way for needed supplies to Yemen, including by delivering large cranes to unload cargo vessels and speed up the process of distributing aid. In a statement on Wednesday, Mr. Young’s office praised the president.

“President Trump’s attention to this critical matter is very encouraging and we hope he continues to pressure the Saudis to fully end the humanitarian blockade of Yemen,” Mr. Young said.

American diplomats had privately pressed the Saudis to relent in their blockade. But Mr. Trump’s silence had prompted criticism that the United States was not doing enough to pressure Riyadh to relent.

“It is a belated recognition that if the blockade is not lifted immediately, an unprecedented humanitarian catastrophe looms, and America is complicit in that catastrophe,” said Bruce O. Riedel, a former C.I.A. analyst and fellow at the Brookings Institution.

In recent days, officials said Mr. Trump was presented with mounting evidence of the human cost of the Saudi blockade, including the impact on children, and the spread of diseases like cholera and diphtheria as a result of the lack of food and clean water in the country.

Officials said that the president and others in the administration grew concerned that private diplomacy with the Saudis was doing too little to relieve the suffering.

Scott Paul, the humanitarian policy lead at Oxfam America, said Mr. Trump’s call for Saudi Arabia to relent is “long overdue but hugely important.” He said in a statement that millions of people could die in an “historic famine” if the Saudis do not agree to pull back from the blockade.