Kenya on Friday charged two men with being members of Somalia's hardline Shabab militia, against whom it launched an offensive nearly two weeks ago in the south of the war-torn country.

Omar Muchiri and Stephen Macharia, both Kenyans, denied the charges. They also denied being accomplices of fellow Kenyan Elgiva Bwire Oliacha, who confessed Wednesday to being a member of the extremist Shebab insurgents.

All three were arrested this week as Kenyan police stepped up security in the wake of Shebab threats to attack the country in retaliation for Nairobi's military offensive in southern Somalia.

The Al-Qaeda-linked group on Thursday called on Kenyan sympathisers to launch attacks against Nairobi, which was this week rocked by two grenade blasts that killed one person and wounded dozens of others.

The Shebab did not claim responsibility of the grenade attacks.

Muchiri and Macharia were detained pending the resumption of their case on November 4.

Kenyan troops rolled into Shebab-controlled southern Somalia on October 16 to fight the insurgents it accuses of a series of kidnappings and attacks on its territory.

Government spokesman Alfred Mutua said Thursday that Nairobi's strategy was to "destroy Al-Shabab's network within the shortest time possible."

"Kenya has no plans or intentions to stay in Somalia an hour beyond necessary," he added, but did not give a time frame.

Kenya's offensive followed the kidnapping of four European women from its soil, all who are believed to have been taken to Somalia by their abductors.