ARMED SOMALI group al-Shabab has claimed responsibility for the attack and ongoing siege of an upscale shopping mall in the Kenyan capital of Nairobi that has left at least 39 people dead and 150 injured.

Kenyan security forces have arrested one of the gunmen who attacked the mall on Saturday, the Kenyan presidency said on Twitter.

The east African country’s head of police, David Kimaiyo, said via Twitter that several other assailants had been pinned down after soldiers and police moved into the mall to hunt down the attackers.

Al Jazeera’s Catherine Wambua-Soi, reporting from Nairobi, said there are reports of an unknown number of hostages being held in the mall, popular with wealthy Kenyans and expatriates.

"We’re told that they’re holding hostages... it’s very difficult for the police and military because they are battling with gunmen who are holding hostages, and who are using these hostages as human shields,” she said.

"What we’re being told is that these gunmen have been isolated in one room and they’re surrounded by police and military and other intelligence services,” said our correspondent, adding that the attackers were wearing bullet-proof vests.

On its own Twitter account, al-Shabab said it had "on numerous occasions warned the Kenyan government that failure to remove its forces from Somalia would have severe consequences”.

Kenyan troops have been fighting al-Shabab in Somalia, where the anti-government group is seeking to impose Islamic law and has carried out numerous attacks.

Kenya has been hit by a spate of attacks including hand grenades and bombs since it sent troops to southern Somalia in late 2011 to attack al-Shabab bases.

Call for unity

In a live television statement, Kenyan President Uhuru Kenyatta said that the country had "overcome terrorist attacks before.”

"In fact, we have fought courageously and defeated them within and outside our borders - we will defeat them again,” said Kenyatta.

"The way we lead our lives in freedom, openness, unity and consideration for each other represents our victory over those who wish us ill,” said the president.

He reiterated the government’s readiness to fight aggression domestically as well as externally, and urged Kenyans to "stand together and see this dark moment through” by donating blood, cooperating with authorities and comforting those affected by the day’s violence.

Kenyatta added that there was a "multi-agency response” to the attacks and that those responsible would be hunted down, "where ever they run to” and be punished for "this heinous crime”.

Lengthy gunbattle

A gunbattle broke out inside the shopping centre as police and military forces struggled to evacuate shoppers and apprehend an unknown number of armed men.

A statement issued later by Kenya’s Internal Security Minister Mutea Iringo said that the government was”fully in charge” of the situation at the mall.

A witness said the attackers opened fire and executed people after they threw grenades into the building at about midday local time (09:00 GMT).

Unverified witness accounts have indicated that the attackers targeted non-Muslims and foreigners.

The US State Department said Americans were reportedly among the injured in the attack, condemning the "senseless act of violence.”

"We have reports of American citizens injured in the attack, and the US embassy is actively reaching out to provide assistance,” spokeswoman Marie Harf said without giving further details.

Agencies