Senior Palestinian official Saeb Erekat is in a critical condition with Covid-19 and has been placed on a ventilator, the Israeli hospital treating him says.
On Sunday, the 65-year-old was rushed to the Hadassah Medical Center in Jerusalem from his home in Jericho, in the occupied West Bank.
His condition was described as "serious but stable", and he was given oxygen.
On Monday morning, the hospital said Mr Erekat's condition had deteriorated and was "now defined as critical".
"Due to respiratory distress, he was put on a ventilator and placed in a medically induced coma," a statement added.
The hospital said treating Mr Erekat was a "huge challenge" because he had undergone a lung transplant three years ago and had a "weakened immune system and bacterial infection, in addition to coronavirus".
Mr Erekat is the secretary general of the Palestine Liberation Organisation (PLO), he serves as an adviser to Palestinian Authority President Mahmoud Abbas and has been the Palestinians' chief negotiator in peace talks with Israel for two-and-a-half decades.
He announced on 9 October that he had tested positive for Covid-19.
He tweeted that he was experiencing "difficult symptoms resulting from my lack of immunity as a result of lung transplantation". But he added that "things are under control, thank God".
On Sunday, the PLO said he had been transferred to Hadassah Medical Center "due to the chronic health problems he faces in the respiratory system".
Witnesses told Reuters news agency that they saw Mr Erekat on a stretcher outside his home in Jericho, being placed in an Israeli ambulance.
His brother Saber told AFP news agency: "His situation is not good."
The director of the Hadassah Medical Center, Prof Zeev Rothstein, said on Sunday: "Mr Erekat is receiving top-notch professional care like all serious corona patients at Hadassah, and the staff will do everything to assist his recovery."
"At Hadassah, we treat every patient as if he were our only patient."
Since the start of the pandemic more than 58,500 confirmed cases of Covid-19 and 478 deaths have been reported in the West Bank, including East Jerusalem, and the Gaza Strip, according to the World Health Organization (WHO).
Israel has meanwhile reported more than 303,000 cases and 2,209 deaths.
On Sunday, Israel's government eased a second nationwide lockdown that has been in place for a month, after seeing a significant decline in the number of new infections.
People in Israel are now permitted to go more than 1km (0.6 miles) from their homes for non-essential purposes, nurseries are reopening, and restaurants are able to serve takeaway food.
Beaches, nature reserves and national parks have also reopened for visitors.
Prime Minister Benjamin Netanyahu said on Thursday that the measures had been a "success" - but that the exit from the lockdown needed to be "gradual, responsible, careful and controlled".