Senior Republican lawmakers and some of President Barack Obama's chief critics in Congress voiced support for Tuesday's US-led air strikes against Islamist radicals in Syria.
The attacks, with the help of Arab states Bahrain, Jordan, Qatar, Saudi Arabia and the United Arab Emirates, opened a new front in the battle against jihadist groups.
Obama called House Speaker John Boehner late Monday to inform him of the operation, and Vice President Joe Biden did the same with other congressional leaders.
"ISIL is a direct threat to the safety and security of the United States and our allies," Boehner said, using one of several names for the Islamic State group that has captured a large patch of Iraq and Syria.
"I support the air strikes launched by the president, understanding that this is just one step in what must be a larger effort to destroy and defeat this terrorist organization," he added.
The Republican support follows bipartisan congressional concern that increased American military action in the Middle East will unleash a third US war in 13 years.
"In times of war and of peace it is important that we come together as a nation," House Homeland Security Committee chairman Michael McCaul said, backing the strikes.
"To defeat ISIS, we must cut off the head of the snake, which exists in Syria," he said
Previously, there were bipartisan assertions that the president would need specific authorization from Congress if he were to conduct broader, sustained US military action in the Middle East.
Those concerns had been muted so far on Tuesday.
Congress last week authorized the Pentagon to begin training and equipping vetted moderate Syrian rebels to battle against IS.
House Foreign Affairs Committee chairman Ed Royce was one of several Republicans who had complained the Obama administration had waited too long before launching military operations in Syria.
"These airstrikes on ISIL's command and training centers are long overdue. With them, the space for these terrorists to operate will shrink," Royce said.
Arguing that the air campaign will need to be "major and sustained," Royce welcomed the participation of Arab allies.
"This is their fight as much as ours," he said.
Republican Senator Marco Rubio said he has argued Obama has executive authority to use military force to confront IS "wherever they seek refuge."
"Defeating this menace to all who value freedom and tolerance will not be easy, but is essential to our security," he said.
With lawmakers currently back home campaigning for re-election, few Democrats had spoken out about the military intervention.
Powerful Senate Armed Services Committee chairman Carl Levin expressed support and hailed the "historic" involvement of Arab nations.
"While Western military force can help combat the poisonous ideology of groups such as ISIS, ultimately it is up to Muslim nations to resist and eliminate this poison," he said.