A draft law before Iraq's parliament that would legalise the marriage of girls as young as nine and restrict women's rights in matters of parenting, divorce and inheritance is a political move to define the identity of the country's majority Shias before next month's election, officials say.

The law, which was approved by Iraq's council of ministers two weeks ago, has generated widespread debate in Iraq six weeks before the first national poll since US forces departed. International human rights groups have described it as a disastrous regression in the status of women.

The 30 April ballot is set to be contested in a cauldron of geopolitical issues, such as the reinvigorated insurgency in Anbar province, the raging war in neighbouring Syria and a continuing dearth of services. But social issues – brought to prominence by the proposed law – are now also likely to feature in the debate, with secular and Islamic leaders anxious to define the social fabric of Iraq's largest sect.

The law was put forward by Iraq's justice minister, who heads the Fadila party, which has seven seats in the national parliament and is allied with the prime minister, Nouri al-Maliki. Its endorsement by the council of ministers was a prerequisite for a vote in the 325-seat assembly. Observers say Iraq's Shia religious authorities are split over how to react to a debate that has roots in Islamic jurisprudence.

Known as the Jaafari personal status law, a reference to the Shia imam of that name, the draft law legalises marital rape and gives men a strict guardianship role over their wives. It also gives automatic custody to fathers in divorce cases that involve children of more than two years old. Most controversially, it allows girls to divorce from the age of nine – a clause that means they must first have been married.

Professor Hassan al-Shimari, a political analyst at Baghdad University, said: "This is an attempt by Fadila to show Iraqis that they represent the Shia and want to make their identity clear before the election. Everything is changing on a daily basis, and the division between the Shia themselves keeps being redefined."

Maliki, who is standing for a third term as leader and is likely to cast himself as the redeemer of a country threatened once again by a Sunni insurgency, has yet to declare his position on the draft law.

He has sent the proposal to committee, a move analysts say is aimed at nullifying it as an election issue, while allowing Maliki to avoid the appearance of conflict with a core part of the Shia constituency.

Iraq's Shia leaders – including Ayatollah Ali Sistani, whom the majority of the country's Shias follow – have so far not weighed into the debate.

Governments in post-Saddam Iraq are typically formed after many months of horse-trading, and there is a sense in Iraq that the law would be seriously considered only if Maliki ended up needing Fadila's support.

"He has never said that he is with the law or against it," said Maliki's spokesman, Ali al-Moussawi. "What we have done is democratic. We took this to be discussed, then voted on. We didn't object straight away.

"Some media outlets show Iraq as if it has gone backwards, but this isn't true. In the west, people are talking about gay marriage. This is something we would never discuss and it is against our religion, our nature, yet we don't say that they are backwards."

A spokesman for the justice minister remained defiant: "There are those who disagree with this law and we don't care about them because they are against Islam. There are ones who think we should modify the law (which will be open to religious interpretation), but for the rest, it is an election campaign and we don't care about what they say.

"Even if this law will be approved, it will be optional for Shia. This law will only be implemented on Shia, and they have the right to take it or not when it is approved."

Safia al-Suhail, one of 82 female MPs in Iraq's parliament, said: "I hope they will put this to a vote in the parliament so it will be rejected by a majority.

"This law means humiliation for women and for Iraqis in general. It is a disaster not just for women but for children. These children shouldn't be exposed to such an ugly situation. It shows that we are going backwards. I hope [the senior Iraqi Shia cleric] Ali al-Sistani will strongly react to it if it is ever taken to the parliament."

Human Rights Watch's Middle East and North Africa deputy director, Joe Stork, said: "Passage of the Jaafari law would be a disastrous and discriminatory step backward for Iraq's women and girls.

"This personal status law would only entrench Iraq's divisions while the government claims to support equal rights for all."