JERUSALEM — Rabbi Yosef Shalom Elyashiv, considered this generation’s leading halachic authority, is in critical condition.

Prayer sessions in Israel and around the world have been held for Elyashiv, 101, the leader of the Lithuanian haredi Orthodox community, since he was admitted to the hospital on Sunday. One on Monday night at the Western Wall attracted thousands of worshipers.

Elyashiv reportedly is on a respirator and has suffered massive organ failure.