Lawmakers loyal to anti-American cleric Muqtada al-Sadr announced Saturday they are withdrawing from the Shiite bloc in parliament — a move that would be a major blow to the government's base in the legislature.

A spokesman for the cleric, Salah al-Obeidi, told reporters that the al-Sadr faction, which holds 30 of the 275 seats, had decided to withdraw from the United Iraqi Alliance because it had not responded to its demands.

The leaves the government of Prime Minister Nouri al-Maliki with a guaranteed total of only 108 seats — 30 short of a majority. However, it could likely also count on support from independent Shiites who hold 30 seats and some minor parties.

But the decision by al-Sadr's followers is likely to complicate further U.S.-backed efforts to win parliamentary approval of power-sharing legislation including the oil bill and an easing of curbs that prevent former Saddam Hussein supporters from getting back their government jobs.

It will also add strains to the Shiite political establishment at a time when armed Shiite groups are competing for power in the Shiite south, which includes major religious shrines and much of the oil resources.

On Tuesday, al-Obeidi told reporters that parliament members loyal to al-Sadr were considering withdrawing from the Shiite alliance because the government has failed to improve services and security.

Al-Sadr's Cabinet ministers left the government in April to protest al-Maliki's refusal to demand a timetable for the withdrawal of U.S. forces.

Tensions came to a boil, however, after arrest warrants wee issued against Sadrist provincial officials in the holy city of Karbala in connection with last month's Shiite factional fighting there.

The warrants, which were made public Saturday, angered the Sadrists who said the government was provoking the group despite recent gestures by al-Sadr such as freezing his Mahdi Army militia's operations for up to six months.

Last month, deadly fighting broke out between rival Shiite militias during a religious festival in Karbala. Up to 52 people were killed in two days of clashes and many blamed al-Sadr's followers for the clashes.