Iraq's parliament adopted a measure on Saturday that would bar Prime Minister Nuri al-Maliki from a third term, a move his allies quickly dismissed as unconstitutional.

A total of 170 MPs of 242 present backed the move to limit the president, premier and parliament speaker to two terms, an official said, meaning Maliki could not retain his post after national elections next year.

But Maliki's supporters insisted the motion was not legally-binding and would be struck down by Iraq's highest courts.

The Sunni-backed Iraqiya bloc, the main Kurdish alliance and the movement loyal to powerful Shiite cleric Moqtada al-Sadr -- all members of Maliki's national unity government -- were the measure's principal backers, said the official, who spoke on condition of anonymity.

Deputy Prime Minister Saleh al-Mutlak, a senior member of Iraqiya, told AFP: "We just want to limit the period the prime minister can serve... so that dictatorship will not start again."

The move appeared to target Maliki, as the speaker of parliament is a member of Iraqiya and Iraq's president is part of the Kurdish alliance.

Iraq's constitution does not set term limits for those posts.

Maliki's supporters in the Council of Representatives insisted the move would be felled by the courts, pointing to a previous ruling by the highest judicial authority that only the cabinet can propose legislation, not parliament.

"The federal court has told the parliament before that they can suggest laws, but they cannot draft laws," said Khaled al-Assadi, a member of Maliki's State of Law Alliance.

"This law will not stand up in front of the courts."

The move to limit Maliki's time in power came after his opponents failed last year to push a motion of no confidence through parliament.

Maliki's opponents -- principally Iraqiya, the Kurdish alliance and the Sadrists -- have accused him of authoritarianism and sectarianism, and have called for him to resign.

The ongoing political crisis has meant no significant legislation has been passed since March 2010 parliamentary elections, and the latest move comes with less than three months to go before key provincial polls.