* Kenya says U.S. flights cancellation unjustified
* U.S. says credible threat to civil aviation in east Africa
By Duncan Miriri
NAIROBI, June 3 (Reuters) - Kenya has summoned the United States ambassador to explain the last-minute cancellation of new Delta Air Lines (DAL.N) flights to the capital Nairobi, a government minister said on Wednesday.
Delta terminated plans to launch four flights a week between Nairobi and Atlanta via Dakar after the U.S. Transportation Security Administration (TSA) failed to clear the new route, citing "noted security vulnerabilities in and around Nairobi".
"It is unjustified ... it amounts to a travel advisory against the country. Yes, I have (summoned the ambassador)," Foreign Affairs Minister Moses Wetangula told Reuters.
Kenya borders Somalia, a lawless country whose 18-year-old civil strife is seen by the international community as offering a haven for al Qaeda-linked militants. Their strongholds are in the south of the country, near Kenya's porous eastern border.
TSA, part of the Department of Homeland Security responsible for the security of America's transportation systems, said it and other federal agencies had been assessing threats to civil aviation in east Africa.
"TSA, along with key partners within the U.S. government, assess a credible threat," it said in a statement.
"At this time, the current threat is too significant to permit these flights. TSA and its partners will continue to closely monitor this situation."
The TSA also blocked Delta flights to Liberia's capital Monrovia, but has cleared a new route to Nigeria's capital.
Delta's flights were eagerly awaited by Kenyan officials hoping to boost tourism and trade as Americans seek to visit the birthplace of President Barack Obama's father and exporters such as horticulture producers seek to diversify their markets.
The Kenyan government said on Tuesday it hoped Delta would soon join other international airlines, such as British Airways, that fly directly to Nairobi.
"The reasons for the postponement by Delta are still not very clear," government spokesman Alfred Mutua said.
"The government of Kenya has complied with all the additional security measures requested by Delta and Nairobi airports' security is excellent," he said.
An al Qaeda truck bomb killed more than 200 people at the U.S. embassy in Nairobi in August 1998. Eleven people were killed in another attack on the U.S. embassy in neighbouring Tanzania on the same day.
Suicide bombers struck again four years later, killing 15 people at an Israeli-owned hotel on the Kenyan coast. At almost the same time, attackers tried to shoot down an Israeli jetliner as it left Mombasa airport. Both missiles missed. (Editing by David Clarke and Jonathon Burch)