Two most wanted Al-Qaeda terror suspects have entered the country, sparking a state of high alert within security agencies.
The suspects, who are also said to be linked to Al-Shabaab, the Somalia rebel group, are among five on the US Federal Bureau of Investigations (FBI) most-wanted list.
They are planning terror attacks in Nairobi and other major towns, according to intelligence reports.
The five on the FBI list have been identified as Jehad Serwan Mostafa, Ahmed Mohammed Hamad Ali, Anas Al-Liby, Abdallah Ahmed Abdullah and Saif Al-Adel.It could not be established which two are in Kenya.
But their presence is said to be the reason the British government on Saturday warned about a possible terror attack in Nairobi.
Police have also stepped up security around vital installations likely to be targets of attacks.
The Al-Qaeda men are being linked to 15 Al-Shabaab members police said left Kismayu recently headed to Kenya. (READ: Police name 15 key Shabaab fugitives)
The group comprises of nine Kenyans, two Asians and four Somalis aged between 24 and 32 years, according to police spokesman Eric Kiraithe.
Mr Kiraithe, who also released the pictures of the suspects on the eve of the New Year, said some of the Kenyans are known to have resided in Majengo area in Nairobi and Mombasa before leaving for Somalia about a year ago.
On Sunday, the Kenya Security Industry Association, a body of private security firms, warned its members about possible attacks.
Chairman Tony Sahni said in a statement that KSIA had received credible intelligence reports that the Somalia militants planned to steal uniforms of private security companies and use them in their attacks.
“With this in mind, we would like to caution members of the public to be vigilant and exercise patience especially when asked to undergo security checks,” he said.
Mr Sahni said KSIA was working closely with the regular and the counter-terrorism police to mitigate the threat.
Mr Sahni told KSIA members to thoroughly vet people seeking employment and increase supervision.
On Saturday, the British government said it believed there was a “heightened” terrorism threat in Kenya and feared the planning of attacks was almost complete.
“The Kenyan authorities have alerted the public to a heightened threat from terrorist attacks in Nairobi. We believe that terrorists may be in the final stages of planning attacks,” a Foreign Office statement said.
Kenya has in the recent past put churches, hotels and shopping malls and other social places under blanket security in an effort to prevent attacks.
This followed their upgrading to a status known in security parlance as “vital installations.”
Normally, vital installations would include airports, military barracks, police stations and foreign missions.
This means the newly upgraded areas will be provided with the same level of security as the sensitive installations.
They will be guarded by armed police officers and be put under round-the-clock surveillance.
Security for Defence minister Yusuf Haji and National Assembly Deputy Speaker Farah Maalim has also been tightened following reports that Al-Shabaab had sent hit squads to eliminate them.
Kenya has been on a state of high alert since its forces crossed into Somalia on October 16 to fight Al-Shabaab.
The rebels threatened revenge attacks, but most have been limited to grenade and improvised explosive devices blasts in Garissa, Wajir and Mandera.
The Kenya Defence Forces says up to 700 militants have been killed in the incursion so far.