Iraq's parliament passed a law on Saturday intended to block Prime Minister Nuri al-Maliki from a third term, as the Shi'ite premier faced growing pressure from mass Sunni street protests.

Lawmakers from Sunni, Kurdish and Shi'ite parties voted for the law, but the legislation still needs the president's approval and will face challenges in federal court after Maliki's supporters rejected it as illegal.

The law, restricting the posts of prime minister, parliament speaker and president to two four-year terms, was approved as the Shi'ite premier tried to end weeks of protests by Sunni demonstrators against his government.

"Parliament succeeded today in passing an important law to limit the terms of three posts, including the prime minister's," said Khalid Shwani, head of the legal panel of parliament.

Parliamentary elections are due early in 2014. First elected in 2005, Maliki was re-elected in 2010 in an indecisive ballot that lead to the formation of a fragile power-sharing government split among Shi'ite, Sunni and Kurdish parties.

Kurdish parties, the Sunni-backed Iraqiya bloc and even some rivals in Maliki's own Shi'ite coalition failed last year to trigger a vote of no confidence against a prime minister they accuse of accumulating power at their expense.

Since the last American troops left Iraq a year ago, Shi'ite, Sunni Muslim and ethnic Kurdish parties have been caught in a power-sharing stalemate that has left key legislation on oil and investment paralysed in parliament.-Reuters