By Cyrus Ombati
The blast happened about 8pm outside a busy mosque along Muratina Road Section I in a busy estate.
Mr Hassan suffered a fractured leg and was taken to the Aga Khan Hospital and the others to the Kenyatta National Hospital, six of them with serious injuries.
He said he had been talking to a group of youths after leaving the mosque when someone threw a grenade at them. The grenade caused a huge crater at the scene.
Deputy speaker Farah Maalim and Makadara MP Mike Sonko are among dignitaries who arrived to visit their injured colleague.
Hassan's bodyguard suffered hand injuries.
The blast sparked violent protests, with rowdy youth barricading roads with burning tyres. Police who included GSU personnel had to fire to the air to disperse the crowd that also attacked even journalists. The group said they wanted to flush out known terrorists who have been operating there.
The situation was contained by police who cordoned off the mosque. The scene of the blast was littered with blood and belongings of the victims.
The attack comes just two days after another that killed one person.
Police had cordoned off the area from the public as they tried to investigate the cause.
The same area suffered a serious blast last month when an IED that had been abandoned in a bus went off killing ten passengers.