The Dadaab refugee camp in Kenya was set up in 1991 to house Somalis fleeing violence in their country [EPA]

An explosion near Kenya's sprawling Dadaab refugee camp near the border with Somalia has wounded at least two security guards who were escorting a convoy of aid workers.

A UN driver said the blast on Tuesday ripped through the back of a police vehicle moments after a column of 10 vehicles had left Hagadera, one of three camps in the expansive complex.

"The police car was at the front of the convoy. As we drove out of Hagadera we saw an explosion at the rear end of the landcruiser," said the driver who declined to be named.

"My car was third in the convoy," he told the Reuters news agency.

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Two refugees from the camp were arrested in connection with the attack, police spokesman Eric Kiraithe said in a statement.

Some witnesses said at least two other police officers were also wounded in the blast.

Abukar Mohamed, a local bus driver, said the blast took place a few hundred metres from the bus park where he was at the time, and sent people scrambling for shelter.

"I then ran to the site of the blast. The two G4S security guards were seriously wounded, they were bleeding all over. The two policemen had minor injuries," he said.

Witnesses said the attack left a two-metre crater in the sand track.

'Wave of attacks'

Kenya has been plagued by a wave of attacks since it sent hundreds of soldiers into neighbouring Somalia last month to crush al-Shabab group.

Dadaab, located about 100 km from the Somali border, was set up in 1991 to house Somalis fleeing violence in their country.

The camp's population has swollen to more than 460,000 people this year because of famine in the lawless country.

The UN's refugee agency, UNHCR, has already cut back its aid operations to essential services, namely distribution of food, water and health care in the camps where cholera has broken out.

Source: Agencies