Story highlights The finding allows for clandestine support for the Syrian rebels, sources tell CNN

When it was signed and what type of support it authorizes are unclear

The Obama administration has resisted arming the rebels in Syria

Several foreign policy experts call for the selective and "wise" arming of some rebel groups

President Barack Obama has signed a covert directive authorizing U.S. support for Syrian rebels battling President Bashar al-Assad 's forces, U.S. officials told CNN on Wednesday.

The secret order, referred to as an intelligence "finding," allows for clandestine support by the CIA and other agencies.

It was unclear when the president signed the authorization for Syria, but the sources said it was within the past several months.

The Obama administration has said it will step up its assistance to the opposition in the wake of last month's failure by the U.N. Security Council to agree on tougher sanctions against al-Assad's regime.

Exactly what type of support the finding authorizes is also unclear. The Obama administration has ruled out arming the rebels for now, providing only nonlethal assistance, such as communications equipment.

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Last week, the U.S. Treasury Department approved a license allowing the Washington Syrian Support Group to provide direct financial assistance to the Free Syrian Army. The Washington-based representative of the Free Syrian Army is allowed to conduct financial transactions on the rebel group's behalf but is not allowed to send military equipment.

During the war in Libya, Obama signed a similar directive authorizing covert assistance for rebels in the battle against Libyan leader Moammar Gadhafi.

The Obama administration has resisted arming the opposition, in part, because U.S. officials don't know enough about the rebels.

U.S. officials have told CNN that Washington is cooperating with countries that are arming the rebels, including Saudi Arabia and Qatar, to help find groups worthy of aid. Diplomatic sources have also said the United States is providing intelligence on Syrian troop movements, which is then passed to rebel groups.

Foreign policy experts on Wednesday urged the Obama administration to increase its support of the armed opposition.

Testifying before the Senate Committee on Foreign Relations, Andrew Tabler of the Washington Institute for Near East Policy argued the United States should start arming the Syrian opposition, but only under the right conditions.

"At this point, given the direction of the conflict, I think that what we need to do is assess which groups could we and should we arm at what point, and make that decision," Tabler told the Senate panel. "I think that we're actually at that decision, given where the conflict is going."

James Dobbins of the Rand Corporation agreed.

"The time has come to consider and pick those groups that are most consistent with our interest and our vision for the future and begin to advantage them in terms of the internal politics, by providing assistance, including perhaps money as well as arms and advice," Dobbins said.

Martin Indyk, a former U.S. ambassador to Israel now with the Brookings Institution, recommended arming the opposition, but in a "wise way."

"We need to do it in a way that, first of all, we understand who we're supporting and what their intentions are," Indyk said.

The State Department said Wednesday the United States has set aside $25 million for "nonlethal" assistance to the Syrian opposition, with another $64 million in humanitarian assistance for the Syrian people.

The humanitarian aid, which includes funding for the World Food Programme, the International Committee of the Red Cross and other aid agencies, helps support the tens of thousands of refugees streaming across Syria's borders to neighboring Turkey and Jordan.