There has been an explosion in a mainly Somali neighbourhood in Kenya's capital Nairobi, police say.Up to nine people were injured in the blast in the Eastleigh neighbourhood, reported to have been caused by a roadside bomb.Last month, a grenade blast in Eastleigh left seven people dead.Kenya accuses neighbouring Somalia's al-Qaeda-linked al-Shabab militant group of trying to destabilise the country.Reuters news agency reports that its correspondent at the explosion site saw pools of blood on the ground, as the wounded were swiftly moved away."The explosion was caused by a roadside bomb which had been placed in a hole in the ground," Nairobi police chief Moses Nyakwama told the AFP news agency."No arrests have been made yet, and investigations are already under way," he added.Al-Shabab has not yet commented on the blast.Last month, Kenya accused the group of launching a grenade attack on a bus in Eastleigh, killing seven people.The attack triggered riots in the area, as angry youths burnt and looted Somali-owned shops.Kenya's government has blamed al-Shabab for a spate of explosions and kidnappings on its territory.Kenyan troops are part of an 18,000-strong African Union (AU) force fighting al-Shabab in Somalia.