JERUSALEM — Shimon Peres, the Israeli former prime minister and president who shared a Nobel Peace Prize for his efforts to resolve the long-running conflict with the Palestinians, remained hospitalized on Wednesday after suffering what his doctor called a “massive stroke.”

Mr. Peres, 93, was sedated and put on a respirator on Tuesday when he was brought to the Israeli hospital, where he suffered the stroke after complaining of a headache.

After an all-night vigil in the hospital, with expressions of sympathy pouring in from around the world, his doctor said Wednesday morning that Mr. Peres was in critical but stable condition and was not in immediate danger of death, although his chances of recovery remained uncertain.

“It’s very emotional, as you can imagine,” the doctor, Rafi Walden, who is also Mr. Peres’s son-in-law, told reporters on a conference call. “We are very close to him, and obviously we are very moved and touched by his condition, but also very moved by the reaction of the public.”