President Trump's Defence Secretary says a Syria strike could cause the conflict to spiral out of control.
US concerns that a military strike on Syria in response to a suspected poison gas attack, could "escalate out of control" have introduced a note of caution in Washington's tone.
US Defense Secretary James Mattis voiced his worries to Congress after saying he believed a chemical attack had taken place in Syria and that such an attack must not go unchallenged.
"There's a tactical concern that innocent people — we don't add to any civilian deaths and do everything humanly possible to avoid that. We're trying to stop the murder of innocent people. But on a strategic level, it's how do we keep this from escalating out of control," Mattis told the House of Representatives Armed Services Committee.
White House press secretary Sarah Sanders was also cautious as President Donald Trump met his national security team.
"We're maintaining that we have a number of options and all of those options are still on the table. Final decisions haven't been made yet on that front," Sanders told reporters.
Those options are still being discussed with allies France and Britain. Trump spoke on Thursday evening with the leaders of both counties. The trio agreed to coordinate an international response hours after UK Prime Minister Theresa May gained her cabinet's backing to take action to "deter the use of chemical weapons."