A series of bombs have exploded outside the Somali parliament killing at least four people, police and Reuters witnesses in Mogadishu say.

Al-Shabab quickly claimed responsibility for Saturday's attack in the Somali capital.

"The so-called Somali parliament is a military zone. Our fighters are there to carry out a holy operation. We shall issue a comprehensive report after the conclusion of the operation," Abdulaziz Abu Musab, al-Shabab's military spokesman, told the AFP news agency.

"A car bomb exploded at the gate of the parliament house - then it was followed by a suicide bomber explosion. So far we have confirmed four policemen dead," Farah Hussein, a police colonel, told the Reuters news agency.

Abdikarim Hussein, a journalist in Mogadishu, told Al Jazeera over the phone that the attack occurred while parliament was in session.

"The fighting has been going on for the past hour," he said.

It was not immediately clear if the attackers had managed to penetrate the parliament complex.

Since being ousted from Mogadishu, al-Shabab has intensified its attacks in Somalia and in neighboring Kenya, which sent troops across the border to fight al-Shabab.

PHOTO CAPTION

Security officers gather around the scene of a car bomb explosion in front of the Parliament building in Mogadishu, Somalia, 24 May 2014.

Al-Jazeera