BAGHDAD, Sept 17 (Reuters) - Iraq's main Shi'ite parliamentary bloc has urged the political movement loyal to anti-American Shi'ite cleric Moqtada al-Sadr to reconsider its decision to quit the ruling Shi'ite Alliance.

A statement, released by the Alliance on Sunday, said the decision by the Sadrists, who hold 30 of the 275 seats in parliament, had taken them by surprise.

The Sadrists pulled out of the Alliance on Saturday, leaving Prime Minister Nuri al-Maliki's government in a precarious position.

"We call on the brothers in the Sadr movement to reconsider their decision and we reiterate the necessity of unity amongst all Iraqi political powers," the statement said.

Maliki's government now has the support of only about half of Iraq's 275 lawmakers.

Senior Sadr official Salah al-Ubaidi said on Monday the movement had received mixed signals from the Alliance over whether it would work seriously to implement Sadrist demands, which included a withdrawal of U.S. forces.

"We have yet to receive an official invitation from the Alliance to restart negotiations. We would be happy to sit and talk over differences, but it's too early to say whether we will return to the Alliance if the results are positive," he said.

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