US Secretary of State John Kerry has urged legislators to adopt a new legal authorisation to underpin military action against Islamic State militants for at least three years.
The call came as US defence chief Chuck Hagel said he has seen "steady progress" in the war on IS, as Iraq appealed for increased military assistance to break the back of the jihadists.
Meeting Hagel in Baghdad on Tuesday, Prime Minister Haider al-Abadi said that Iraqi forces were advancing on the ground against IS fighters who have seized large parts of the country.
During a heated debate on Tuesday in Washington, Kerry came under fire from Republicans and Democrats who argued that if President Barack Obama wanted new powers to combat the jihadists, he should have drawn up a draft text to propose to the Senate.
The US-led coalition has already carried out about 1100 air strikes in Syria and Iraq since September targeting IS extremists.
So far, the Obama administration has used the existing authorisation for use of military force against al-Qaeda, the Taliban and their branches approved in the days after the September 11, 2001 attacks as the legal justification for going after IS.
Kerry told the Senate foreign relations committee: "I think we all agree that this discussion must conclude with a bipartisan vote that makes clear that this is not one party's fight against ISIL (IS), but rather that it reflects our unified determination to degrade and ultimately defeat ISIL.
"Our coalition partners need to know it. The men and women of our armed forces need to know it. And ISIL's cadres of killers, rapists, and bigots need to understand it."
He asked the committee to help draw up a new authorisation which "provides a clear signal of support for our ongoing military operations against ISIL", referring to the group by another acronym.
Kerry also urged that the text should not limit US actions geographically to just Syria and Iraq, and suggested it should be valid for three years with room for a possible extension.
Controversially, the top US diplomat also appealed to senators not to rule out the use of ground troops.
Obama has insisted he will not send US ground troops into combat operations against IS, saying that "will be the responsibility of local forces".
"That does not mean we should pre-emptively bind the hands of the commander-in-chief - or our commanders in the field - in responding to scenarios and contingencies that are impossible to foresee," Kerry said.
While the Obama administration did not plan to carry out any operations with the 60-strong coalition outside of Syria and Iraq, Kerry argued the new legal authority should "not constrain our ability" to act in other places if needed.
"In our view, it would be a mistake to advertise to ISIL that there are safe havens for them outside of Iraq and Syria," he told senators.
Committee chairman Robert Menendez has a draft text ready for a vote, which he suggested could go ahead on Thursday.
He said he was "not comfortable" with the current reliance on the 2001 authorisation and a 2002 vote for the invasion of Iraq.
The three-and-a-half-hour hearing also provided a golden opportunity for senators to bash US strategy in the region.
