Iraq's parliament postponed until Monday a vote on controversial legal amendments, including a reworked family law bill that had sparked civil outrage over fears of a resurgence in underage marriages.

A session devoted to the legislation scheduled for Sunday did not go ahead and would now be held the following day, parliament's communications department said.

The proposed amendments would let people choose between religious or state regulations for family matters, such as marriage, inheritance, divorce and child custody.

Critics fear the move could erode protections for Muslim women by lowering the legal age for marriage -- currently set at 18, or 15 with the consent of legal guardians and a judge -- and pave the way for the adoption of Islamic jurisprudence that could allow girls as young as nine years old to marry.

A revised version of the bill sets the minimum age at 15 with court approval and retains "current conditions", according to MP Raed al-Maliki, who backs the new proposals.

Couples could opt for Shiite Muslim or Sunni Muslim rules under the amendment.

If passed, clerics and lawyers would have four months to establish community-specific regulations. Parliament would then vote again to finalise the changes.

The draft law has already undergone two readings, with votes previously delayed.

An earlier version faced a backlash from feminists and civil society groups.

In October, Amnesty International warned the amendments could legalise unregistered marriages -- often used to bypass child marriage bans -- and strip protections for divorced women.

The London-based rights group also voiced concerns that the amendments would strip women and girls of protections regarding divorce and inheritance.

But Sunday's session was postponed over disagreements on another bill that was under review, concerning a general amnesty law.

"The point of contention concerned the amnesty law," MP Hussein Mouanes told AFP.

"Several times, parliament has tried to organise a session to (vote) on certain controversial laws, but each time it has failed due to disagreement between the political blocs," he added.

Iraq's Sunni community has been the main proponent of reviewing the amnesty law, which according to Maliki excludes convictions for around 20 offences, including "terrorism", rape, incest, human trafficking and kidnapping, according to Maliki.

Sunni MPs have been pushing for a full review of all convictions on "terror" charges, Maliki said.

"It's impossible... we can't force the judiciary to reopen investigations in cases 15 years after a verdict," he continued.

But, he noted, cases based on evidence from "secret informants" may qualify for retrial.

In recent years Iraqi courts have ordered hundreds of executions in "terror" cases, proceedings that rights groups say often lack due process or in which confessions suspected to have been extracted through torture are admissible.

A previous 2016 amnesty reportedly covered 150,000 people.