A boot belonging to a soldier loyal to Libyan leader Muammar Gadhafi is seen on a destroyed tank after an air strike by coalition forces, along a road between Benghazi and Ajdabiyah on Monday. [Photo/Agencies]

WASHINGTON / New York - United States President Barack Obama is facing growing criticism at home and abroad over whether the military campaign in Libya is the wrong policy - or the right policy at the wrong time.

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Within the US, Congress is divided on the issue, including some high-profile Republicans who have raised concerns over the no-fly zone.

Obama, on a five-day tour of Latin America, defended his administration's muscular approach in Libya, saying it was "very easy to square our military actions and our stated policies".

Obama sent a letter to congressional leaders on Monday attempting to assure them that the administration was seeking a "rapid but responsible transition" of military command to other members of the United Nations-backed coalition. The letter followed complaints that he had failed to consult Congress before taking military action.

Republican Senator Richard Lugar, a veteran leader on foreign policy, earlier warned against the establishment of a no-fly zone over Libya and said the president must seek a congressional declaration of war.

Republican Congressman Ron Paul has said the no-fly zone over Libya is an "act of war", and it needs approval from Congress.

Among Democrats, Congressman Dennis Kucinich has called Obama's decision to launch air strikes against Libya "impeachable".

Younes Abouyoub, a research scholar in Middle Eastern, South Asian and African Studies at Columbia University in New York, said a no-fly zone should have been put in place earlier to help the rebels fight Gadhafi's forces.

But he warned that "the UN needs to make sure that this intervention does not become a military occupation lest we end up with a scenario like Iraq or Somalia".

"Libyan people need help, but they should be allowed to decide for their future alone and in complete independence," he said, adding the next immediate step should be an official recognition of the rebel leadership as the sole legitimate representative of the Libyan people.

Several US scholars have called on "clear objectives" of the strikes.

Robert Danin, senior fellow for Middle East and Africa Studies at the Council on Foreign Relations, wrote: "With the United States now militarily engaged in Libya, it is imperative that the president refine the nation's objectives more clearly and the means that will be employed to achieve them."

"Failure to clarify them entails running afoul of our coalition partners, a slide into an open-ended military engagement or an unintended expansion of the mission," he noted.

A group of liberal Democrats, including Representatives Jerrold Nadler of New York, Donna Edwards of Maryland, Dennis Kucinich of Ohio and Maxine Waters and Barbara Lee of California, issued a statement over the weekend saying they "all strongly raised objections to the constitutionality of the president's actions".

Some conservatives, as well as foreign policy experts, said Libya is not a vital US interest.

An ant-iwar group announced plans for protests in Los Angeles, Chicago and nine other cities this week.

"The president seems to have angered almost every major group. He's either done too much or too little or he's done it too slowly," the Los Angeles Times quoted James Lindsay, a former official in the Clinton White House who is now with the Council on Foreign Relations, as saying. "There's a very real political risk for Barack Obama in all of this."

Complaints also came from the Arab League, which initially called for imposing a no-fly zone in Libya, a decision that helped persuade the White House to join the fight. Russia's prime minister, Vladimir Putin, lashed out at Washington for launching what he called "a crusade", saying it justified Russia's military buildup.

Administration officials acknowledged the political risk of involvement in Libya at a time when the US is engaged militarily in Iraq and Afghanistan, and polls indicate that Americans want Obama to focus on the economy.