Updated

The Obama administration lent its support Monday to British and French plans to arm Syria's rebels, saying it wouldn't stand in the way of any country seeking to rebalance the fight against an Assad regime supported by Russia, Iran and Hezbollah.

Secretary of State John Kerry said the longer Syria's two-year civil war goes on, the greater the danger of its institutions collapsing and extremists getting their hands on the Arab country's vast chemical weapons arsenal. With some 450,000 Syrians living in neighboring countries as refugees already, he said the conflict is becoming a "global catastrophe."

Kerry said the world needs to change Syrian President Bashar Assad's calculations.

"If he believes he can shoot it out, Syrians and the region have a problem, and the world has a problem," Kerry told reporters after a meeting with Australian Foreign Minister Bob Carr.

Kerry said the U.S. wants to leave the door open for a political solution. But concerning Syria's rebels, he added, "the United States does not stand in the way of other countries that made a decision to provide arms, whether it's France or Britain or others."

The comments come after French President Francois Hollande said last week that his country and Britain were pushing the European Union to lift its arms embargo on Syria as soon as possible so that they can send weapons to rebel fighters. The two countries are seeking military help for the rebels by the end of May or earlier if possible. But Germany and other EU nations have been skeptical about sending weapons, pointing to the risk of further escalation in a volatile region.

The United States long held the same conviction, with President Barack Obama and other officials saying more weapons in Syria would only make peace harder. As the violence has worsened over the last year, Washington has tempered that message somewhat. It is now promising nonlethal aid to the anti-Assad militias in the form of meals and medical kits, and refusing to rule out further escalation.

And support for greater U.S. involvement appears to be growing in Congress. On Monday, the top Democrat on the House Foreign Affairs Committee introduced legislation to train and arm vetted Syrian opposition forces.

The groups must be opposed to Assad, willing to establish a peaceful and democratic Syria and committed to securing and safeguarding chemical and biological weapons. No aid could go to a group associated with a foreign terrorist organization, according to the bill by Rep. Eliot Engel of New York.

"It is time for us to develop a comprehensive approach to stopping the carnage," he said in a letter to his colleagues last week.

At the State Department, Kerry said there is a fundamental imbalance in Syria's civil war. The Assad regime is attacking with tanks, scud missiles and aircraft that the rebels don't have. And Kerry said Russia, Iran, Hezbollah and al-Qaida-related elements are helping Assad.

With al-Qaida and its allies, it's unclear what support the secretary of state was describing. Al-Qaida in Iraq has clearly backed Syria's rebels, which has been acknowledged by U.S. and other Western officials, particularly through its relationship with Jabhat al-Nusra — which the U.S. has declared a foreign terrorist organization.

Millions of people have been pushed from their homes by the violence. The U.N. says more than 70,000 people have been killed.

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Associated Press writer Donna Cassata contributed to this report.