Kenya's security chiefs on Tuesday ordered that defences be boosted around the capital's airport, including against possible missile attack amid "increased threats of radicalisation" from homegrown Islamist extremists.

The country's top defence body, the National Security Council (NSC), demanded extra protection around Nairobi's Jomo Kenyatta International Airport (JKIA).

Kenya has suffered a string of attacks blamed on Islamist insurgents, including the September massacre in Nairobi's Westgate mall in which at least 67 people were killed

Somalia's Al-Qaeda-linked Shebab said the Westgate attack was a warning to Kenya to pull its troops out of southern Somalia, where they are fighting the Shebab as part of an African Union force.

The NSC "approved the construction of an integrated security screening facility" on the approach to the JKIA terminals, east Africa's largest international flight hub, presidential spokesman Manoah Esipisu said in a statement.

The defence boost will also bring together security forces protecting the jet fuel depot and the "operations base camp for protection against the threat of Man operated Anti-Aircraft Devices (MANPADS) on low flying aircraft," Esipisu added.

Four Somali men are awaiting trial for a failed attack in January at a cafe at the airport, which police had initially dismissed as an exploding light bulb.

Security checks at the entrance of the airport have been significantly beefed up since the blast, which injured no one.

The NSC, which met Tuesday, is headed by the president and includes the chiefs of the armed forces, intelligence and police among others.

It also warned of an "increased prevalence of radicalisation centres", including a mosque in Nairobi and two in the main port city of Mombasa, where supporters have clashed several times with security forces in recent years.

The "NSC further noted with concern the impact of radicalisation on the political economic, social and security well-being of Kenya."

Homegrown groups including the Islamist Al-Hijra group, a radical organisation formerly known as the Muslim Youth Center, operate on Kenya's coast and have been linked to the Shebab.