The United States is using its pilotless drone aircraft to launch military attacks on leaders of the Somali militant group, Al Shabaab, the Washington Post reported Thursday.

The Post quoted an unidentified U.S. official as saying a drone fired on two Al Shabaab leaders last week, apparently wounding them.

The official was reported to have said of Al Shabaab: "They have become somewhat emboldened of late, and, as a result, we have become more focused on inhibiting their activities... They were planning operations outside of Somalia."

The Post said Somalia joins Afghanistan, Pakistan, Libya, Iraq and Yemen as the objects of lethal attacks from drones.

In remarks made in Washington on Wednesday, President Barack Obama's assistant in charge of counter-terrorism, John O. Brennan, identified Somalia as a country which hosted "affiliates and adherents" of Al Qaeda.

"As the al-Qa'ida core has weakened under our unyielding pressure," Brennan said, "it has looked increasingly to these other groups and individuals to take up its cause, including its goal of striking the United States...

"...[U]ltimately defeating al-Qa'ida also means addressing the serious threat posed by its affiliates and adherents operating outside South Asia," he added.

"From the territory it controls in Somalia, Al-Shabaab continues to call for strikes against the United States. As a result, we cannot and we will not let down our guard. We will continue to pummel al-Qa'ida and its ilk, and we will remain vigilant at home."

Agence France-Presse reports that residents of the port town of Kismayo in southern Somalia heard loud explosions on Thursday last week, followed by the sound of aircraft.

The agency quoted an unnamed Al Shabaab official as saying that "the military aircraft of the enemy carried out an aerial bombardment on a base where some mujahedeen fighters were staying... We believe the aircraft belonged to the U.S".