Several US lawmakers led by Republican Senator Rand Paul introduced legislation Tuesday that would finally bring to an end Washington's authorization to wage war in Iraq.

President Barack Obama's White House backs the efforts, in principle, having withdrawn US forces in December 2011.

Obama has declared the war over, yet a loophole in the law green-lighting the March 2003 invasion allows for future US presidents to send troops back to Iraq, still a turbulent country.

A bill spearheaded by Paul, a libertarian who consistently seeks to scale back foreign intervention by US forces, and backed by several Democrats would repeal the authorization, known as an AUMF.

"Two years ago, President Obama declared the war in Iraq over," Paul said.

"With the return of our troops and practical side of the mission concluded, I feel it is necessary to bring the war to an official and legal end."

Paul, a potential 2016 presidential candidate, has clashed with Obama over national security, notably on the use of military drones, but the White House backs the senator's latest position.

"The administration supports the repeal of the Iraq AUMF since it is no longer used for any US government activities," National Security Council spokeswoman Caitlin Hayden said in a statement.

"We understand that some in Congress are considering legislation related to the Iraq AUMF, and we will certainly examine these proposals as they come forward."

A US official said the White House has not actively sought to repeal the AUMF "because the effect would be entirely symbolic, and we have many more pressing priorities to take up with Congress."

But Democratic supporters of the two-page bill, including Senator Kirsten Gillibrand, said closing the book on an "open-ended" war resolution was a key check on a commander-in-chief's power.

"No president, Democrat or Republican, should have a blank check when it comes to war," Gillibrand said.

The legislation brings together an unlikely band including arch-conservative Senator Mike Lee and liberal Senate stalwart Ron Wyden.

One of 23 senators who refused to vote for the Iraq war resolution back in 2002, Wyden said it "makes sense" to end the AUMF now.

"While sectarian conflict and violence still persist in Iraq, it must be the Iraqis -- not the men and women of the US military -- who now make the difficult choices, forge a stable and inclusive political order and steer their country to peace and prosperity."

In October 2002, by more than two to one, US lawmakers authorized president George W. Bush to use military force to oust Iraqi president Saddam Hussein.

The resulting 2003 invasion has haunted US politics for years, with Bush administration claims, including Hussein's weapons of mass destruction and alleged links with Al-Qaeda, widely discredited.

But Iraq has seen a surge in influence by the terror network, whose Islamist insurgents have taken over the city of Fallujah, where US troops faced some of the fiercest fighting in their nine years in Iraq.

Critics of the White House blame Obama for failing to agree a deal with premier Nuri al-Maliki's government to leave a residual US force behind after withdrawing all American troops at the end of 2011.

Earlier this month Secretary of State John Kerry said the United States backed Iraq in its battle against militants but stressed a return of US forces was not part of the equation.