The Trump administration is slapping new sanctions on Somalia’s al-Shabab extremist group, an al-Qaida-linked organization responsible for multiple terrorist attacks in East Africa.

The State Department announced it had imposed sanctions on two senior leaders of the group, which had been designated a “foreign terrorist organization” in 2008.

The State Department said it had identified Abdullahi Osman Mohamed and Maalim Ayman as “specially designated global terrorists,” a step that freezes any assets they may have in U.S. jurisdictions and bans Americans from doing any business with them.

It said Mohamed is the group’s senior explosives expert, a special adviser to the so-called “emir” of al-Shabab and is the leader of al-Shabaab’s media wing, al-Kataib. Ayman is the leader of Jaysh Ayman, an al-Shabab unit conducting attacks and operations in Kenya and Somalia, including one in January on a military base in Kenya that killed one American soldier and two U.S. contractors, it said.

Al-Shabab remains the most active and resilient extremist group in Africa, controlling parts of southern and central Somalia and often targeting checkpoints and other high-profile areas in the capital, Mogadishu. It has fired several mortars this year at the heavily defended international airport, where the U.S. Embassy and other missions are located.

It has also branched out to stage attacks in neighboring counties, including Uganda and Kenya, where it was behind the days-long 2013 attack on Nairobi’s upscale Westgate Mall that left 67 people dead.

Earlier this month, the U.N. Security Council voted to extend an arms embargo on Somalia and ban the sale or shipment to Somalia of components for improvised explosive devices if there is “significant risk” they may be used to manufacture the devices that are increasingly being used by al-Shabab. It also urged the Somali government to crack down on the group’s illegal financing methods.