The United States is dispatching Army planners to Jordan as neighboring Syria's conflict worsens, US Defence Secretary Chuck Hagel said on Wednesday, but he signaled deep misgivings about direct American military intervention in the Syrian civil war.

Hagel told a Senate hearing that the United States has an obligation to think through the consequences of any US military move in Syria and be honest about potential long-term commitments.

His comments were the latest indication that while President Barack Obama's administration continues to plan for various scenarios in Syria, it remains wary of an intervention that could mire America in a proxy war.

"You better be damn sure, as sure as you can be, before you get into something. Because once you're into it, there isn't any backing out, whether it's a no-fly zone, safe zone ... whatever it is," Hagel told senators.

"Once you're in, you can't unwind it. You can't just say, 'Well, it's not going as well as I thought it would go so we're gonna get out.'"

Hagel said the Pentagon was sending an Army headquarters unit to Jordan, bolstering efforts started last year to plan for contingencies related to Syria's chemical weapons and to prevent a spillover of violence across Jordan's border.

A US official told Reuters that the total number of American planners in Jordan would remain roughly at 200 because an existing team is largely being withdrawn.

Still, the deployment of the headquarters unit - which could theoretically command combat troops - was seen as an enhancement over the previous ad hoc team of planners, the official said, speaking on condition of anonymity.

In Amman, a Jordanian official said the team would "increase the level of preparedness and defense capabilities in light of the continued deterioration in the Syrian situation."

Syria is expected to top the agenda when Hagel leaves on Saturday for a trip to the Middle East that will take him to Jordan as well as Israel, Saudi Arabia, Egypt and the UAE.

"There is a regional consensus I think you will find on your trip, Mr. Secretary, that they want American leadership," Senator John McCain of Arizona, an advocate of US intervention in Syria, said at the hearing.

"And I think if you visited one of the refugee camps or met with the opposition, which I hope you will, they are angry and bitter because we haven't helped them."

March was the bloodiest month yet in a conflict that began as a protest movement against four decades of Assad family rule but has descended into an increasingly sectarian civil war in which at least 70,000 people have been killed.

Sunni Muslim rebels are the backbone of the insurgency, while minorities like the Alawites, from an offshoot of Shi'ite Islam, have largely fought with Syrian President Bashar al-Assad, who can count on support from Russia and Iran.

Western powers, who want to see the end of Assad but do not want to intervene militarily, have been alarmed by the advance of Islamist groups like the Nusra Front in a conflict that has deepened the Middle East's sectarian divide.

General Martin Dempsey, chairman of the Joint Chiefs of Staff, last year had favored the idea of arming Syrian rebels, as did Hagel's predecessor, Leon Panetta, and the heads of the CIA and State Department.

But Obama decided against it. On Wednesday Dempsey said the current opposition presents an even more confusing picture than it did six months ago.

"Now I am more concerned than I was before" about the prospect of arming them, he said.

When pressed whether he would still favor arming rebels, he said: "If we could clearly identify the right people, I would support it."

Assad on Wednesday accused the West of supporting al Qaeda militants in Syria's civil war and warned they would turn against their backers and strike "in the heart of Europe and the United States.

"The West paid heavily for funding al Qaeda in its early stages in Afghanistan," he told Syria's al-Ikhbariya channel, drawing parallels with Western support for anti-Soviet fighters in Afghanistan in the 1980s.

"Today it is supporting it in Syria, Libya and other places, and will pay a heavy price later."-Reuters