LONDON — Pressure was growing on Prime Minister al-Maliki of Iraq yesterday as it emerged that 150 people may have died in a bomb attack on a northern village over the weekend and that critics were preparing a no-confidence motion in Parliament.

Mr. Maliki denounced the bombing in the town of Amirli in northern Iraq as a “heinous crime.” A truck packed with high explosives was driven into the very center of a busy market, where it exploded in the thick of a crowd, killing at least 130 people.

The blast was so powerful that 20 buildings were also leveled. Officials have been unable to count all of the bodies, and a local police chief, Brigadier Abbas Mohammed Amin, said the death toll could be as high as 150, making it the worst single incident in Iraq since April.

Amirli is a mixed town, populated by Sunnis, Shiites, and members of Iraq’s Turkoman ethnic minority. As such, it is a classic target for Sunni extremists, many of whom have left Baghdad to escape the “surge” of American reinforcements.

Mr. Maliki also called on the Mahdi army, the Shiite militia loyal to the radical cleric Moqtada al-Sadr, to lay down its arms. The prime minister claimed fighters loyal to Saddam Hussein’s Baath Party had infiltrated this group. Mr. Sadr’s followers have been elected to parliament and are part of Mr. Maliki’s ruling coalition. The fact that he defied them by making this call — in accordance with frequent American demands — betrays the pressure the prime minister is under.

The American news channel CBS reported that Mr. Maliki could face a motion of no confidence in Parliament. A block of Sunni politicians, calling themselves the Iraq Project, is thought to be behind the move.

Tariq al-Hashimi, the vice-president and Iraq’s most senior Sunni politician, may be involved. He is believed to have discussed the plan with Vice President Cheney, who recently visited Baghdad. Mr. Hashimi has been deeply critical of Mr. Maliki, accusing him of marginalizing Sunnis and turning a blind eye to Shiite militias.

In a recent interview, he said: “Cosmetic change is not going to serve the interests of Iraqis, is not going to stabilize, is not going to improve security. What we need is much bigger that that.”

America may try to use the possibility of a confidence vote to compel Mr. Maliki to take further steps against Shiite militias. The prime minister’s latest remarks about the Mahdi army indicate that this could be having an effect.

Three more attacks took place yesterday. Another truck bomb killed 23 army recruits east of Fallujah. In the Karrada area of Baghdad, once populated largely by Christians, two car bombs left eight dead.