Four people have been charged over the siege at the Westgate shopping centre in Kenya's capital, Nairobi, in which at least 67 were killed, police say.

The four foreigners have been charged with aiding terrorist groups and being in Kenya illegally.

Their nationalities have not been disclosed, but they are said to be ethnic Somalis.

These are the first charges to be brought in relation to the four-day September siege.

Those charged have been named as Mohammed Ahmed Abdi, Liban Abdullah, Adnan Ibrahim and Hussein Hassan.

"The accused persons carried out a terrorist attack at Westgate Shopping Mall on 21 September by supporting a terrorist group," the charge sheet read.

The police say the four accused had sheltered the attackers in their homes in Eastleigh - a Somali neighbourhood in Nairobi - and that they were in contact with the gunmen four days before the siege.

All four, who had no lawyer, have pleaded not guilty to the charges, which also included obtaining false identification documents.

None of the men is accused of being the gunmen in the centre.