Kenya has imposed a curfew in Lamu three days after fighters from the Islamist militant group al-Shabab stormed into a military base, killing three Americans.The curfew will begin daily at 22:00 until 04:00 local time (19:00-01:00 GMT) for an indefinite period.It is intended to help security agencies to monitor suspicious activity, the Star newspaper reports.The coastal region Lamu is close to the Somali border where al-Shabab has been fighting the UN-backed government.County police chief Muchangi Kioi is quoted in the Star as saying that no vehicles will be allowed to operate during the curfew period, and that police will conduct security searches on vehicles during the day.Sunday's attack on the military base saw vehicles and aircraft destroyed.Residents are reported to have fled villages that are located near the base out of fear of more attacks.Last week, three passengers were killed in the area when heavily armed men stopped a bus and sprayed it with bullets. Two others were injured and were rushed to local clinics.