At least two people were killed when a bomb exploded on Monday in a busy market in Somalia's capital Mogadishu at the start of Islam’s holy month of Ramadan, police said.

"The explosive device was planted under a pile of rubbish near a police post," police officer Abdi Bare told AFP.

Al-Qaida-linked Shebab militants have warned they will step up attacks in the Somali capital Mogadishu during the holy month of Ramadan, which started on Sunday.

In an audio message released on the Shebab-controlled station Radio Andalus and also on an Islamist website, the group's commander in charge of Mogadishu operations, Sheik Ali Mohamed Hussein, said the time had come when violence will be at a peak. 

Al-Qaida-linked Shebab commandos on Thursday attacked an African Union military base in central Somalia dressed in stolen government army uniforms, killing at least two soldiers from Djibouti, the AU force said.

The Shebab said their gunmen stormed the compound of a hotel where Djiboutian troops with the AU force were based in the town of Bulla Burde, some 200 kilometers (125 miles) north of the capital Mogadishu, their spokesman Abdulaziz Abu Musab told AFP.

A Danish court on Monday cut a prison sentence given to two Danish brothers of Somali origin convicted for attending a training camp run by Somalia's Islamist Shebab rebels.

A court in the central city of Aarhus cut the jail sentence for Guleed Mohamed Warsame, 25, and Nuur Mohamed Warsame, 20, to two years from three and a half years for conspiring to send, and sending, the 25-year-old to a Shebab-run training camp in Somalia.

At least 20 people have been killed in Kenya in ethnic clashes in the restive northeast, the latest in a series of revenge attacks between rival Somali clans.

Fighting broke out on Sunday between clans in the Tarbaj district of Wajir along the border with war-torn Somalia, government officials said on Monday.

Somalia's Shebab rebels on Wednesday repeated claims they were responsible for two consecutive massacres in Kenya, the day after Kenya's president insisted that "local political networks" and not the Al-Qaida-linked group were to blame.

"The attack in Mpeketoni was ordered by the mujahedeen high command to retaliate for Kenya's killing of Muslims in Somalia and Kenya. The Islamic fighters answered to that holy call," Shebab's military spokesman, Abdulaziz Abu Musab, said in a news conference broadcast by Shebab's radio.

A doctor was killed on Wednesday and two others wounded when a car bomb exploded at a hospital in Somalia's capital Mogadishu, staff and witnesses said.

The bomb, believed to have been attached to a car belonging to a doctor, blew up at Keysansey hospital in northern Mogadishu, which is run by the Somali Red Crescent Society with support from the International Committee of the Red Cross (ICRC).

Kenyan President Uhuru Kenyatta on Tuesday blamed "local political networks", and not Somalia's Shebab militants, for the killings of dozens in two consecutive nights of attacks in the coastal region.

"This... was not an al-Shebab attack. Evidence indicates that local political networks were involved in the planning and execution of a heinous crime," he said in a televised address to the nation. "This also played into the opportunist network of other criminal gangs."

Suspected Shebab militants from Somalia stormed into a Kenyan coastal town, killing at least 49 people in a major assault on a police station, hotels and government offices, officials said Monday.

Around 50 heavily-armed gunmen drove into the town of Mpeketoni, near the coastal island and popular tourist resort of Lamu, late on Sunday, officials said.

Malaysia's navy has fought off a pirate attack on a tanker off its east coast in the South China Sea, the International Maritime Bureau said Sunday.

The Malaysian force was assisted by the Indonesian and Singaporean navies in fending off the attack late Saturday, said Noel Choong, head of the IMB's Kuala Lumpur-based Piracy Reporting Center.