The United States said Monday it has not ruled out any option to bring about the departure of Syrian President Bashar al-Assad, following renewed speculation about a possible no-fly zone.

White House spokesman Jay Carney was asked about comments by US Secretary of State Hillary Clinton in Turkey that sparked a new round of questions about a stepped-up Western role in the violence-wracked country.

“The president and his team have ruled out no option as we try to bring about, with all of our partners and with the Syrian people, the diplomatic transition that is so desperately needed in Syria,” he said.

But Carney did not explicitly refer to a no-fly zone and insisted the current US approach — of aiding rebels with non-military supplies as well as imposing sanctions on the regime — was putting pressure on Assad.

“We review all options as you would expect and will continue to do so,” he said, in comments which did not seem to mark a new departure for US policy.

On Sunday, Clinton was asked after talks with Turkish Foreign Minister Ahmet Davutoglu whether operational planning being conducted by Washington and its allies included a possible no-fly zone to protect Syrian civilians.

“The issues you posed in your question are exactly the ones the minister and I agreed need greater in-depth analysis,” she said.

“It is one thing to talk about all kinds of potential actions, but you cannot make reasoned decisions without doing intense analysis and operational planning,” she added.

Washington insists Assad must leave office as part of any solution to the 17-month-old civil conflict in Syria, which has left more than 21,000 dead.

But there appears to be little appetite in Western capitals for another military intervention in the Middle East, even the imposition of an aerial exclusion zone like that imposed in Libya by NATO last year.

US military officers have warned that the imposition of a no-fly zone could quickly escalate into a broader intervention, as it did in Libya.

The Pentagon on Monday said the Syrian regime was employing more air power in its war with the rebels.

“We’ve seen a very troubling and despicable uptick in attacks from the air, perpetrated by the Syrian regime,” Pentagon spokesman George Little told reporters.

“This is yet another example of their depraved behavior.”

Asked if the Pentagon was moving towards enforcing a possible no-fly zone, he said: “We plan for contingencies.”

He added: “The focus right now of course is ending the bloodshed in Syria.”