Palestinian President Mahmoud Abbas cut ties with both the United States and Israel on Saturday amid anger at Donald Trump's peace plan.
Abbas made the announcement at a special meeting of Arab League foreign ministers in Cairo.
"We are informing you that there will be no relations with you and the United States, including on security cooperation," he said, referring to Israel.
The US has proposed granting the Palestinians only limited self-rule in parts of the occupied West Bank.
The plan would also allow Israel to formally annex all its settlements in the West Bank. They're considered illegal under international law.
The Western-backed Palestinian leadership has been under mounting pressure from ordinary Palestinians and its rivals in the Islamic militant group Hamas to cut off security ties with Israel and the U.S. or even dismantle the increasingly unpopular Palestinian Authority.
That would leave Israel responsible for the complicated and expensive task of providing basic services to hundreds of thousands of Palestinians in the West Bank.
The Palestinians have made such threats in the past, with few people taking them seriously. But this time might be different, especially if Israel proceeds with annexation of its West Bank settlements as well as the Jordan Valley, which accounts for roughly a fourth of the West Bank, according to the U.S. plan.
There was no immediate comment from U.S. or Israeli officials on Abbas' statement.