The Central Intelligence Agency is expanding its role in the campaign against the Syrian regime by feeding intelligence to select rebel fighters to use against government forces, current and former U.S. officials said.

The move is part of a U.S. effort to stem the rise of Islamist extremists in Syria by aiding secular forces, U.S. officials said, amid fears that the fall of President Bashar al-Assad would enable al Qaeda to flourish in Syria.

The expanded CIA role bolsters an effort by Western intelligence agencies to support the Syrian opposition with training in areas including weapons use, urban combat and countering spying by the regime.

The move comes as the al Nusra Front, the main al Qaeda-linked group operating in Syria, is deepening its ties to the terrorist organization's central leadership in Pakistan, according to U.S. counterterrorism officials.

The provision of actionable intelligence to small rebel units which have been vetted by the CIA represents an increase in U.S. involvement in the two-year-old conflict, the officials said. The CIA would neither confirm nor deny any role in providing training or intelligence to the Syrian rebels.