The British government has raised the threat level for travel to Kenya to critical.
The Foreign Office said on Saturday it believes terrorists may be in the final stages of planning attacks and warned visitors to avoid places such as hotels, shopping centres and beaches.
British nationals were strongly advised to exercise extra vigilance and caution in public places and at public events.
Kenya sent troops into Somalia in October after a series of kidnappings and cross-border attacks which had threatened Kenya's tourism industry.
The Kenyan army is engaged in military action against al-Shabab fighters in southern Somalia. The BBC reports they are linked to al-Qaeda.
The Foreign Office warning was issued warning after the Kenyan army said it had killed 60 Somali al-Shabab fighters in air strikes and was determined to "break their spine completely".
But al-Shabab responded by promising to defeat the Kenyans.