ISLAMABAD, Pakistan (AP) -- Gunmen opened fire on Shiite Muslim worshipers as they knelt in prayer at a mosque in eastern Pakistan Monday, killing 16 people and wounding at least 25.

As many as 13 of the wounded were believed to be in critical condition, police said.There was no immediate claim of responsibility for today's attack. But police said they feared it was part of the relentless violence between rival Shiite and Sunni Muslim sects that has killed hundreds of people in Pakistan, mostly in Punjab province.

Today's attack in the village of Quereshi More, 180 miles south of the eastern Punjab provincial capital of Lahore, occurred as 100 Shiite worshipers were finishing morning prayers that marked the beginning of their day-long fast.

Devout Muslims fast from sunrise to sunset during the holy month of Ramadan.

The attackers, who were riding motorcycles, sprayed the mosque with bullets as they sped past, eyewitnesses said. There were apparently as many as four motorcycles, with two men on each motorcycle, they said.

Eyewitnesses recounted emotional scenes of neighbors rushing to the mosque, grabbing small children and old men, cradling the dead and comforting the wounded.

The attack came one day after an unsuccessful assassination attempt against Prime Minister Nawaz Sharif at a bridge near his private residence in a town outside Lahore. The blast killed four people and ripped apart the bridge Sharif was supposed to have crossed, but he and his family were still at home because of a delay.

Police blamed the ethnic Muttahida Qami movement for the attack on the bridge. There was no evidence the mosque killings were connected to the assassination plot.