Kenyan police on Sunday morning shot dead two terrorist suspects in a security operation, which took several hours in a residential estate in Nairobi, the capital of East Africa's largest economy.

Nicholas Kamwende of the regional Criminal Investigations Department (CID) said six police officers were injured in a grenade attack during the security operation in a house in Githurai residential estate in Nairobi.

"The suspected identified as Paul Wangaga and his wife were shot dead after they threw three grenades at officers who wanted to arrest them on Saturday night," Kamwende told journalists at the scene in Nairobi on Sunday.

The police said they suspect the deceased planned to carry out a terror attack in the city and its environs after several months of lull in such attacks in Nairobi due to increased security surveillance at all entry points.

The East African nation is facing a great challenge in dealing with the "enemy within", who has executed several terror attacks undetected as Kenya Defense Forces and its allies effectively fight external aggressors -- Al-Shabaab in southern Somalia.

Kamwende linked the two terror suspects who were shot dead early on Sunday to Elgiva Oliacha Bwire who hurled grenades at a crowded bus park on March 10, 2012 in Nairobi.

The police tracked and arrested a Kenyan, 28-year-old Oliacha, alias Mohammed Seif, who confessed he committed the crimes and was a member of the Al-Shabaab group.

Oliacha, who has since been jailed for life, was also found with an AK-47 rifle, a submachine gun, two revolvers, 13 live hand grenades and 770 assorted rounds of ammunition.

Subsequent efforts to fight terrorism and neutralize Al-Shabaab threats have seen Anti-Terrorism Police Unit arrest dozens of other Kenyans on suspicion of being members of the Somali terror group.

It is such suspects, and dozens others, born and bred in Kenya and who are believed to be sympathizers of Al-Shabaab that the East African nation is grappling with in its fight against terror.

Police have said most of those who are being used to carry out terror attacks in Kenya are its own youth, who have been enlisted in the Somali-based extremist group.

Most of them are from upcountry Kenya and are recent converts to Islam, as in the case of Oliacha, alias Mohamed Saif, Nderitu aka Mohammed and Muchiri, alias Hussein.