Nairobi, Kenya (CNN) -- U.S. officials in Kenya have warned of an "imminent threat" of a terror attack on Mombasa and urged Americans to leave the port city.
Mombasa, the second-largest city and a major tourist spot for the East African nation, is one of various cities targeted by a series of grenade attacks in recent months.
The U.S. Embassy in the capital, Nairobi, said it has suspended all U.S. government travel to Mombasa until July 1.
"All U.S. government personnel are required to leave Mombasa," the embassy said in a statement Friday. "U.S. private citizens are not subject to the same restrictions, but should consider this information in their travel planning."
The warning did not elaborate on the threat or why it targeted the port city.
Kenyan forces invaded southern Somalia in October to battle Islamist militant group al-Shabaab, which it blamed for attacks and kidnappings of foreigners in the nation. The terror group has threatened Kenya with retaliatory attacks, saying it considers the forces' incursion an affront to Somalia's sovereignty.
Since the invasion, Kenya has been targeted by a series of grenade attacks blamed on the terror group or its supporters.
Al-Shabaab is linked to al Qaeda and has been designated a terrorist organization by the United States.
The embassy has issued other warnings of potential attacks in the country since Kenya sent its troops to Somalia.
Follow our coverage of national and global security on CNN's Security Clearance blog.
CNN's David McKenzie contributed to this report.