The Obama administration on Thursday named three leaders of the Nigerian militant group Boko Haram and a Basque separatist commander to the U.S. terrorism list.

State Department spokeswoman Victoria Nuland described Boko Haram leaders Abubakar Shekau, Abubakar Adam Kambar and Khalid al-Barnawi as "kingpins" of the radical Islamist group that claimed responsibility for last year's deadly attack against a U.N. building in Nigeria's capital of Abuja.

The department called Shekau the group's "most visible" leader. It said Kambar and al-Barnawi have forged close ties with al-Qaida.

"Shekau has publicly stated the goal of overthrowing the government of Nigeria and an interest in instituting strict Shariah," or Islamic law, in the country, Nuland told reporters Thursday.

Designating these men as global terrorists blocks any assets the men may have in the U.S. and bars Americans from doing business with them. Nuland did not say if the U.S. had located any funds in the U.S.

The administration also added Aitzol Iriondo to the list for alleged involvement in killings on behalf of the Basque group ETA, which long has sought a homeland in parts of Spain and France. The group is already considered a terrorist organization by the U.S.

Iriondo is in custody in France, awaiting extradition to Spain. He faces murder and terrorism charges.

Nuland called Iriondo's designation "a sign of our political solidarity with the government of Spain as it continues to go after ETA."

The U.S. has yet to issue a blanket terrorism designation against Boko Haram, however.

The group claimed responsibility on Thursday for launching multiple attacks in Nigeria, which authorities say killed at least 40 people. The violence was the latest manifestation of sect-related tensions in the West African country. At least 138 have died since Sunday.

Nuland said U.S. officials were studying whether to blacklist Boko Haram entirely.

She said the administration was also working with Nigeria's government and communities to encourage "a real dialogue about some of the roots of the dissatisfaction" in Nigeria's predominately Muslim and largely impoverished northern areas.