NAIROBI (AFP) - Kenyan police on Monday released four people, including three minors, arrested over weekend grenade attacks that killed six in the capital Nairobi, the suspects' lawyer said.

"Sylvester Opiyo and the three minors have been released," said Chacha Mwita, referring to a man who had been on a police wanted list arrested alongside the youngsters Sunday.

Mwita said the four had been ordered to report to the anti-terrorism police on Tuesday.

"Police have indicated to them why they were being held and why they are being investigated," added the lawyer.

The grenade attack on Saturday also wounded more than 60 people when assailants threw four grenades at a busy bus station in downtown Nairobi as they drove past in a car.

Somalia's extremist Shebab rebels whom Kenya blamed for the attack, denied involvement but renewed a warning that they would target Kenya for its offensive against the Al Qaeda-linked insurgents in southern Somalia.

The blasts were the deadliest in Nairobi since one in June 2010, not attributed to Islamists, during a public meeting against the adoption of a new constitution in which six people died.