The amended oil bill -- a key plank in efforts to help unite the country's warring communities -- was endorsed by Prime Minister Nuri al-Maliki's government on Tuesday and forwarded to parliament for a first reading.

Parliament was however unlikely to handle the legislation on Wednesday as initially expected.

"The reading of the draft oil is not on the agenda of the parliament session today," Khalid Attiya, acting speaker of Iraq's 275-member parliament, told AFP.

The northern Kurdish administration, a key party to the negotiations on the legislation, said it had "not seen and approved the final text of the law."

"We hope that the cabinet is not approving a text with which the KRG (Kurdish Regional Government) disagrees because this would violate the constitutional rights of the Kurdistan Region," a statement from the northern regional administration said.

The draft law was first approved by the Baghdad cabinet in February but Iraq's warring Shiite, Sunni and Kurdish factions later demanded a number of amendments.

The Kurdish administration said it was uncertain as to which version of the law was approved on Tuesday, although Iraqi government spokesman Ali al-Dabbagh said the latest text contained only linguistic changes to the February draft.

"While the KRG is happy with the legal committee's language improvements and restructuring of the legal text, we reject its changes to the substance of the law," the Kurdish government said.

"If it has agreed to the version that included material and substantive changes, the KRG rejects this document. We have not been informed which text the Iraqi cabinet has approved."

It was unclear how many ministers were present at Tuesday's cabinet meeting, as six ministers from the Moqtada al-Sadr group and six ministers from the Sunni bloc are currently boycotting the government.

A number of foreign companies have already entered into contracts with the Kurdish government and the Kurds fear that the new law may lead to the termination of the deals.

In May, Oil Minister Hussein Shahristani said any contract signed before the adoption of law would be cancelled.

Kurdish officials say they will honour the contracts and also claim to have reached an agreement with Baghdad whereby it will receive 17 percent of the country's oil revenues.

Leaders from Iraq's main Sunni Arab political bloc, the National Concord Front, also expressed concern over the latest bill.

"The Front did not receive any official information of the draft. We do not know anything about the latest copy which was endorsed by the cabinet," said lawmaker Ala Makki from Iraqi Islamic Party, the key faction in the Front.

"If our brothers want to pass the law without the Front's opinion then it is their affair and it is up to them. We are not responsible for it."

Iraq's oil reserves are largely in the Kurdish north and the Shiite south and the Sunni Arabs from the central and western regions fear they could be robbed of the revenues from the crude exports.

The draft law lays down control of the country's oil wealth and how it would be distributed across the communities.

Oil exports are Iraq's single most important source of revenue, even after more than four years of frequent insurgent attacks on oil facilities.

US officials have repeatedly urged Iraqis to adopt a consensus law on sharing revenues and on international investment in order to head off future conflict and allow the oil sector to develop.

Iraq's proven oil reserves, estimated at 115 billion barrels, are thought to be the third largest in the world, but since the US-led invasion production has tumbled from 3.5 million barrels per day to around two million.