Chief Palestinian negotiator Saeb Erekat, hospitalised in Israel with COVID-19, was placed on a ventilator on Monday after his condition deteriorated, a spokeswoman for the facility said.
Erekat was rushed to Jerusalem's Hadassah Medical Center on Sunday from his home in the occupied West Bank. He contracted the coronavirus on Oct. 8.
Erekat, 65, is considered especially vulnerable to the illness because he underwent a lung transplant in the United States in 2017, which suppressed his immune system.
"Mr. Erekat had a quiet night but this morning his condition deteriorated, and it is now defined as critical," a statement from Hadassah spokeswoman Hadar Elboim said.
"Due to respiratory distress, he was put on a ventilator and placed in a medically induced coma," it added.
The statement said Erekat was also being treated for a bacterial infection.
A member of Fatah, the most powerful faction within the PLO, Erekat has been one of the most high-profile faces of the Palestinian leadership for decades, especially to international audiences.
Erekat, who is also secretary-general of the PLO, is one of the most senior advisers to Palestinian President Mahmoud Abbas, and also served in top positions under Abbas' predecessor, Yasser Arafat.
A proponent of a two-state solution of the Israeli-Palestinian conflict, Erekat has been a leading Palestinian voice in opposing Israel's settlement policy in territory it captured in the 1967 Middle East war.