US lawmakers have written to Palestinian Authority President Mahmoud Abbas warning him to do something about the violence perpetrated on Israel or risk losing out on humanitarian aid to the region.

"US law clearly stipulates that the Palestinian Authority must act to counter the incitement of violence against Israelis in order to continue receiving US assistance," the letter, from politicians from both sides of the House, said.

"This aid is predicated on the Palestinian Authority's commitment to countering terrorism and pursuing a comprehensive peace with Israel. We remain resolute in our commitment to these conditions."

The letter was signed by politicians including Rep. Hal Rogers, the chairman of the US House of Representatives Appropriations Committee, Rep. Nita Lowey, the chief democrat on the committee and Rep. Kay Granger, the chairwoman of the committee's foreign operations subcommittee.

"The use of degrading images in Fatah or PA produced media as well as inflammatory language used by you and other Palestinian leaders undermine the objectives of our support and threaten to further destabilize an already highly volatile situation," the letter continued.

The United States currently donates financial assistance of approximately $500m (£319m) to the Palestinian Authority a year.

Palestinian Authority President Mahmoud Abbas strongly condemned the recent killings of four Jewish worshippers and a Druze policeman at a West Jerusalem synagogue but his apology was criticised for not going far enough.

"The presidency condemns the attack on Jewish worshippers in their place of prayer and condemns the killing of civilians no matter who is doing it," his office said in a statement.