The U.S. has delayed paying about $125 million to the United Nations agency that serves Palestinian refugees, said two people familiar with the matter, after President Donald Trump vented his frustration about getting no "respect" or help in the peace process despite American funding.

The U.S., by far the biggest contributor to the U.N. Relief and Works Agency (UNRWA), had been expected to deliver the payment on Tuesday. But Secretary of State Rex Tillerson put a hold on the funds while the administration reviews its next steps, said one of the people.

The delay could be purely symbolic, since the U.S. has a few more weeks before it must make the payment. But the delay is a break from past practice, when such funds were delivered promptly at the start of the year.