AMMAN, Jordan -- Right after the United States formalized its backing of a new Syrian opposition group Wednesday, the mutual unease underpinning the partnership surfaced as the group’s leader openly criticized the United States for declaring the rebel movement’s Nusra Front a terrorist group linked to al Qaida in Iraq.

Sheik Moaz al Khatib, head of the Syrian National Coalition of Revolutionary and Opposition Forces, asked the Obama administration to rethink its labeling of the Nusra Front, stressing that the militant faction was integral to the fight against the regime of President Bashar Assad.

“The logic under which we consider one of the parts that fights against the Assad regime as a terrorist organization is a logic one must reconsider,” Khatib told reporters in Marrakesh, Morocco, after more than 100 nations agreed to recognize his group as the “legitimate representative” of the Syrian people.

Khatib’s tacit endorsement of Nusra was echoed by many rebel commanders inside Syria and signals a thorny road ahead as U.S. officials attempt to disentangle nationalist or relatively moderate rebel factions from the Islamist extremists who have become perhaps the leading military force in the nearly two-year fight to topple Assad.

“We love our country. We can differ with parties that adopt political ideas and visions different from ours. But we ensure that the goal of all rebels is the fall of the regime,” added Khatib, a Muslim cleric who’s complained in the past that blueprints for a post-Assad transition were too secular.

U.S. officials did not react to Khatib’s statements, but Deputy Secretary of State William Burns said in Morocco that Khatib had been invited to visit Washington soon.

Burns also announced a $14 million aid package to assist millions of Syrians who've been forced from their homes by fighting and now face the onset of winter. The package includes "essential medicines, nutritional supplements for over 200,000 children, and blankets and boots for thousands of families," he said.

Mapping out the disparate rebel ideologies is an urgent matter because of signs that the conflict is escalating. For months, pro-Assad forces and rebels had been locked in a bloody, lopsided war of attrition that’s cost an estimated 40,000 lives since the conflict began in March 2011 as part of the Arab Spring protest movement.

In recent weeks, however, the rebels have gained ground with sophisticated operations, typically spearheaded by Nusra fighters, including some who’d fought U.S. forces in Iraq. The regime is fighting back hard, continuing its campaign of shelling and bombing rebellious areas. Opposition activists who compile casualty figures say at least 200 Syrians died on Tuesday alone, a number that could not be independently verified.

Nusra’s likely significance in the conflict was on display again Wednesday when three blasts at the front gates of Syria’s heavily guarded Interior Ministry in Damascus devastated the building and reportedly killed four people and wounded at least 20.

No group immediately claimed responsibility, but self-proclaimed Nusra fighters posting on militant forums on the web said that the explosions were a Nusra operation. Nusra has taken responsibility for at least 40 suicide blasts inside Syria in the past year, the State Department said earlier this week. It was a pair of massive bombings in Damascus nearly a year ago that first prompted U.S. officials to conclude that al Qaida in Iraq had moved its operations to Syria.