WASHINGTON -- Lobbyists for the Free Syrian Army will meet with members of Congress and staffers from both political parties in a closed-door meeting on Tuesday morning in an effort to persuade the U.S. government to provide weapons and training to the rebel group, according to emails from House staffers obtained by The Huffington Post.

The Free Syrian Army is frequently referred to as a "moderate" militant group in the Syrian civil war, one opposed to both Syrian President Bashar al-Assad and to hardline groups such as the Islamic State, also known as ISIL or ISIS. President Barack Obama has proposed arming and aiding the Free Syrian Army as part of a U.S. offensive against the Islamic State, which controls a broad swath of territory in Syria and Iraq.

The complexity of the conflict in Syria has many lawmakers in Washington wary of literally providing more ammunition to the fight. The forces in favor of toppling Assad include not only relatively moderate organizations, but also extremists such as the al-Nusra Front -- a branch of al Qaeda -- and even the Islamic State itself. Conflicting recent reports have suggested that many of these groups, moderate and otherwise, have agreed to stop fighting each other and to focus on toppling Assad. It is not clear that the Free Syrian Army is part of any such agreement, and the White House has denied that such a truce exists.

Adding to the confusion in Washington is the recent statement from Free Syrian Army founder Col. Riad al-Asaad that his organization will not support American efforts to destroy the Islamic State unless it receives help from the U.S. to overthrow Assad.

Lobbyists for the Free Syrian Army will meet with House members and staff at 10 a.m. Tuesday. The meeting is closed to the press and to House interns.

Obama has said he has authority to act against the Islamic State without congressional approval, but some members of Congress question whether that claim has a legal basis, particularly with regard to action in Syria. The Authorization for the Use of Military Force that Congress passed in September 2001, many critics note, gives the president powers against al Qaeda and those that aided them in carrying out the Sept. 11 attacks. The Islamic State did not exist in 2001 and has split from al Qaeda.

A new vote to authorize the Obama administration's efforts in Syria and Iraq would eliminate that dispute, and also force members of Congress to back publicly the president's war plan. The Obama administration has been conducting airstrikes against the Islamic State in Iraq for some time and describes the United States as being "at war" with the group.

House Republicans may offer restricted legislation giving the administration authority under Title X of the U.S. Code to arm and train Syrian rebels for a limited time, but not give Obama additional powers. The administration requested the Title X measure from Congress last week.