(CNN) — A bomb blast rocked Somalia’s newly reopened national theater in the capital city Wednesday, killing two top sports officials.

Witnesses reported other casualties, but it was unclear how many.

Said Mohamed Mugambe, head of the Somali football federation, and Somali Olympic committee chief Adan Hagi Yabarow Wish were killed in the attack, a hospital official told CNN.

The bomb went off during a celebration for the first anniversary of Somali national television in Mogadishu, according to witnesses. Screaming people fled the theater and ambulance sirens filled the air.

The African Union Mission in Somalia said the device had been detonated by a female suicide bomber who blended in with the crowd gathered for the occasion.

Several civilians were killed and injured but no Somali government ministers were hurt, the group said in a statement.

The Islamist group Al-Shabaab, which has been waging war against Somalia’s weak transitional government, claimed responsibility for the bombing via Twitter.

A post to the group’s Twitter page said the explosives had been planted before the gathering and denied that a woman had carried out the attack.

Brig. Gen. Audace Nduwumunsi, deputy force commander of African Union Mission in Somalia, condemned the bombing.

“We are united with the Somali government and stand firm together. This was a despicable crime against the Somali people, but it will not stop us achieving peace in Somalia,” he said.

“Yet again the terrorists’ methods show that they are enemies of peace and are foreign to Somali culture. By their attack they are trying to derail the hopes and dreams of the Somali people but they will fail.”

He urged anyone in Mogadishu with information about planned attacks to come forward.

Last month, a suicide bomber detonated himself at a tea shop near Somalia’s presidential palace. Two people were killed.

Al-Shabaab also claimed responsibility for that attack.

CNN’s Nima Elbagir contributed to this report.