VIENTIANE, Laos (AP) _ A bomb on a parked bicycle exploded at the airport in the Lao capital of Vientiane on Thursday, injuring at least four people, diplomats said.

The bomb went off outside the domestic air terminal at Wattay airport just outside the city, diplomats and a United Nations employee said, all on condition of anonymity.

Four Lao women sitting on a bench near the terminal entrance were injured and sent to the hospital, a diplomat said.

There were unconfirmed reports that several other passers-by were injured, but it appeared no foreigners had been hurt, diplomats said. The government was not immediately available for comment.

The crude homemade explosive, which contained shards of metal, had been placed in a plastic bag on the back of a bicycle, diplomats said, the same method used in a May bombing outside a Vientiane hotel.

Thursday's blast was the latest in a series of at least nine mysterious bomb explosions in Vientiane since late March, normally one of Asia's most placid capital cities. Dozens of people, including foreigners, were injured. No one has claimed responsibility.