Long-time chief Palestinian negotiator Saeb Erekat, diagnosed with coronavirus, was taken to an Israeli hospital on Sunday after his condition worsened, the Palestine Liberation Organisation and his brother said.
The PLO said in a statement that Erekat was "transferred to Hadassah hospital in Jerusalem", updating a previous announcement that he had been taken to a facility in Tel Aviv.
"Following his contraction of Covid-19, and due to the chronic health problems he faces in the respiratory system, Dr Erekat's condition now requires medical attention in a hospital," it said.
"His situation is not good," his brother Saber Erekat told AFP.
The PLO said on October 19 he had tested positive for the virus.
There have been 42,490 confirmed cases of the novel coronavirus in the West Bank, including 381 deaths.
Erekat, who lives in the biblical town of Jericho, in the Israeli-occupied West Bank, underwent lung-transplant surgery in the United States in 2017.
The 65-year-old has been a key figure in Palestinian politics for decades, often serving as a main interlocutor for foreign envoys and the international media.
He has consistently voiced support for a two-state solution to the Israeli-Palestinian conflict.
The Jerusalem-born Erekat serves as the PLO's secretary-general and remains a stalwart presence in the inner circle of Palestinian president Mahmud Abbas.