"Where possible, Kenyans are strongly advised to watch the World Cup matches from the comfort of their homes instead of crowded and unprotected open places," the interior ministry said in a statement.
"Although the government has beefed up security in all parts of the country, bar and restaurant owners are at the same time notified to maintain high alert in their areas of operation," the statement said.
"This will ensure that bar and restaurant patrons are safe from criminals who may try to take advantage of the World Cup to perpetrate acts of criminality and violence."
The attack came as some people in the town were watching a World Cup match in local cafes and hotels.
A further nine people were killed in an attack the following night in a nearby village.
The attacks were claimed by Somalia's Al-Qaeda-linked Shebab, although President Uhuru Kenyatta has instead blamed the carnage on "local political networks" along with an "opportunist network of other criminal gangs".