WASHINGTON — The United States is looking at delivering non-lethal aid to Syria's rebels, Defense Secretary Leon Panetta said Wednesday, hinting at the first direct US assistance to forces seeking President Bashar al-Assad's downfall.

While the United States is outraged at the killing of civilians it does not believe in taking "unilateral" military action and favors pursuing diplomacy to force Assad to step down, Panetta told the Senate Armed Services Committee.

Asked by Senator Richard Blumenthal if the United States was ready to deliver communications equipment to Syrian rebels, Panetta said: "I'd prefer to discuss that in a closed session but I can tell you that we're considering an array of non-lethal assistance."

His answer marked the first time President Barack Obama's administration had suggested it was ready to provide direct assistance to Syria's rebels, who are badly outgunned by the regime's tanks and artillery.

The Pentagon chief's comments came as UN humanitarian chief Valerie Amos said the Syrian protest city of Homs had been "completely devastated" and that the regime had prevented her from visiting opposition-held areas.

Panetta condemned the regime's violent crackdown but expressed caution about military intervention, citing a lack of international consensus, a deeply divided resistance and the risk of fueling a civil war.

"We are reviewing all possible additional steps that can be taken with our international partners to support efforts to protect the Syrian people, end the violence, and ensure regional stability, including potential military options if necessary," Panetta said.

"Although we will not rule out any future course of action, currently the administration is focusing on diplomatic and political approaches rather than a military intervention."

Some Republican lawmakers, including Senator John McCain, have called for US air strikes to support the Syrian rebels and warned that time is of the essence to protect threatened civilians.

"Syria today is the scene of some of the worst state-sponsored violence since the Balkans," McCain said at the hearing.

The "only realistic way" to stop Assad's artillery and tanks is through "foreign air power," he said.

Panetta, however, echoed Obama's view that the situation was different than Libya, where a NATO-led coalition carried out a bombing campaign last year that helped topple Moamer Kadhafi's regime.

In the case of Libya, there was strong support for intervention in the UN Security Council and within the Arab League, he said. But Russia and China have opposed punitive measures and the Arab League has stopped short of endorsing an air war over Syria.

Panetta also said the armed resistance in Syria was so fragmented that it was difficult to know who outside governments should recognize or contact, with roughly 100 groups identified as part of the opposition.

"It is not clear what constitutes the Syrian armed opposition -- there has been no single unifying military alternative that can be recognized, appointed, or contacted."

Resorting to military action could have the unintended effect of feeding a full-blown civil war, he said.

Syria's Russian-made missiles and radars could pose a challenge for any air campaign, officials say, and the US military's top officer, General Martin Dempsey, said air defenses in the country's west are five times more powerful than Libya's anti-aircraft weaponry.

Advocates of intervention, however, have cited a successful air strike -- widely believed to be the work of Israel's air force -- that knocked out a secret nuclear reactor in Syria in 2007.

The American military role has so far been limited to sharing intelligence with regional partners, Dempsey said. "But should we be called on to help secure US interests in other ways, we will be ready," he said.

"We maintain an agile regional and global posture. We have solid military relationships with every country on Syria's borders," said Dempsey, the chairman of the Joint Chiefs of Staff.

The military had prepared contingency plans for possible intervention at the request of the White House, but the president has not yet been briefed and a more detailed operational plan has yet to be drawn up, he said.

The military options include imposing a no-fly zone, naval "interdiction" and "limited aerial strikes," he said.