Powerful Iraqi Shia cleric Muqtada al-Sadr has called for a sit-in starting next Friday at the gates of Baghdad's heavily fortified Green Zone to put pressure on Prime Minister Haider al-Abadi to deliver on political reforms.

The cleric said last month that Abadi had 45 days to deliver on his pledge of a technocrat cabinet, or face a no-confidence vote in parliament.

In a statement on his website, Sadr on Saturday called for a sit-in starting on March 18 until the end of the 45-day period, which falls at the end of the month.

The Green Zone houses government offices, parliament, foreign embassies and international organisations.

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The statement came a day after tens of thousands of protesters heeded a call by Sadr to take to the streets of the Iraqi capital for the third week in a row to demand a political overhaul.

In a pre-recorded speech aired during the demonstration, Sadr said: "I urge Iraqi Prime Minister Haider al-Abbadi to press on with plans to form an independent cabinet of technocrats, to fight graft despite political pressure to desist.

"I want the prime minister to continue his reform plan with no fear of political pressure."

Last month, Abadi, now a year and a half into his four-year term, said he wanted to replace his ministers with technocrats to challenge the system of patronage that encourages graft by distributing posts along political, ethnic and sectarian lines.

Sadr and his supporters have held regular demonstrations demanding reforms to tackle corruption, which is eating into Baghdad's resources even as it struggles with falling revenues due to a slump in global oil prices and high spending caused by the costs of war against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS).

Source: Agencies