At least 20 people have been killed and several others wounded in twin suicide blasts in the central Somali town of Galkayo, according to a Somali health official.

The first vehicle explosion on Sunday targeted the local government headquarters; the second targeted emergency services at the scene of the first blast.

"There were two huge bombs. The first one was a truck bomb, followed a minute or so [later] by another car bomb. My brother was injured at the scene," Halima Ismail, a local resident, told Reuters news agency.

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Authorities initially put the death toll at 13, including civilians and security forces personnel, but a medical official said that number had risen.

"Death toll is over 20 and it may rise further," said Ahmed Sugule, a doctor at Galkayo hospital. He said another 30 people were wounded in the attack.

Al-Shabab, the armed group fighting to overthrow the internationally backed government in Mogadishu, claimed responsibility for the blasts.

The UN mission in Somalia condemned Sunday's explosions. "Terrorist attacks will not stop 2016 electoral process," UNSOM said via its Twitter account.

Somalia is scheduled to hold elections later this year.

The attack in Galkayo comes just days after Somali security services captured a wanted al-Shabab commander there.

US-trained commandos called Danab arrested Abdullah al-Sudani and four other suspected fighters.

Source: Al Jazeera and agencies