UPDATE 1-US seeks ways to boost African forces in Somalia

* U.S. looking at ways to provide 'more robust' support

* Official: 'aggressive action' needed to thwart groups

* Drones are not part of the plan, but may be considered (Recasts with counterterrorism official, paragraph 2, 4-6)

By Adam Entous

WASHINGTON, July 20 (Reuters) - The United States is prepared to step up assistance to African Union forces in Somalia and take more aggressive action against al Shabaab Islamist rebels who carried out deadly bombings in Uganda earlier this month, U.S. officials said on Tuesday.

U.S. intelligence agencies have warned of growing links between al Shabaab in Somalia and al Qaeda's network in East Africa, and the Obama administration has made it a priority to track and target top militants in both groups, officials said.

The expanded U.S. military assistance to African Union forces could include additional equipment, training, logistical support and information-sharing, said General William Ward, commander of U.S. Africa Command.

A U.S. counterterrorism official, speaking on condition of anonymity, suggested lethal operations targeting al Shabaab could expand as well.

"This terrorist group is primarily focused on targets in the region, but we can't discount its aspirations to conduct operations elsewhere," the official said, calling connections between al Shabaab and al Qaeda in Africa "deeply troubling."