U.S. airstrikes bombarded an al-Shabab training camp in Somalia Saturday, killing more than 150 militant fighters who were preparing to launch a large-scale attack, likely against African or U.S. personnel, the Pentagon said Monday.

Lisa Monaco
In this Feb. 13, 2015 file photo, Assistant to the President for Homeland Security and Counterterrorism Lisa Monaco speaks in Stanford, Calif. U.S. (AP Photo/Jeff Chiu, File)

Multiple drones and manned aircraft launched missiles and bombs on the site, called Raso Camp, which the U.S. had been watching for several weeks, said Navy Capt. Jeff Davis, a Pentagon spokesman.

News of the attack comes as the White House announced Monday that it will disclose how many people have been killed by American drones and other counterterrorism strikes since 2009, when President Barack Obama took office.

Lisa Monaco, Obama's counterterrorism and homeland security adviser, said the report will be released "in the coming weeks," casting it as part of a commitment to transparency for U.S. actions overseas.

Monaco said the figures would be disclosed annually in the future, although it will ultimately be up to Obama's successor to decide whether to continue the practice.

The report will include both combatants and civilians the U.S. believes have died in strikes.

It won't cover major warzones like Iraq, Syria and Afghanistan, but will focus on strikes against extremist targets in other regions such as Pakistan, Libya, Yemen, Somalia and other locations in North Africa.

"We know that not only is greater transparency the right thing to do, it is the best way to maintain the legitimacy of our counterterrorism actions and the broad support of our allies," Monaco said at the Council on Foreign Relations.

The Pentagon on Monday provided some details about the Somalia strike, which happened during the early evening there. Davis said it appeared that the training was about to come to an end, and the operational phase of a suspected attack was about to start.

Military forces from the U.S. and the African Union Mission in Somalia (AMISOM) are routinely working in the country, and Davis said they could have been the targets of al-Shabab's planned attack.

The camp, located about 120 miles north of Mogadishu, was destroyed, Davis said, adding that the U.S. believes there were no civilian casualties.

He said the U.S. estimated that as many as 200 fighters had been at the camp, including a number of trainers.

The al-Qaida-linked al-Shabab has been linked to a number of attacks, including the detonation of a bomb aboard a commercial passenger jet last month that forced the plane to make an emergency landing in Mogadishu.

While sketchy details often emerge about individual drone strikes, the full scope of the U.S. drone program -- conducted by both the Defense Department and the CIA -- has long been shrouded from view. And the new report is not likely to answer all of the questions.

The U.S. doesn't publicly disclose all the places its drones operate, so the report isn't expected to detail specific countries where people died.

Instead, it will offer an aggregate assessment of casualties outside of areas of "active hostilities" -- a designation that takes into account the scope and intensity of fighting and is used to determine when Obama's specific counterterrorism policies apply. Iraq and Syria, where U.S. airstrikes are pummeling the Islamic State group, currently are on that list and won't be in the report, said a senior administration official, who wasn't authorized to comment publicly and requested anonymity.

"There will obviously be some limitations on where we can be transparent, given a variety of sensitivities -- including diplomatic," said White House spokesman Josh Earnest.

Obama's move to shed more light on the drone wars comes as the U.S. struggles to contain extremist groups and violent ideologies that are growing and spreading. For example, the Islamic State group that the U.S.-led coalition is fighting in Iraq and Syria is spreading to under-governed places in Libya and Afghanistan, and is spawning affiliates and recruits around the world.

Monaco, the counterterrorism adviser, described the strikes as one tool in a fight against terrorism that has entered a new, unpredictable phase nearly 15 years after the 9/11 attacks.

In place of top-down, well-organized groups like al-Qaida, the threat has shifted to a diffuse array of smaller groups and lone actors in what Monaco dubbed "do-it-yourself terrorism."

"What keeps me up at night is that this threat is unlike what we've seen before," she said.

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