Kenya says its troops in Somalia have exchanged fire with al-Shabab militants in the first direct clash between the sides.

A Kenyan military statement says Kenyan troops were attacked by about 45 al-Shabab fighters Thursday as the troops moved toward the southern Somali town of Qoqani to reinforce forward positions.

The statement says Kenyan forces killed nine al-Shabab members and injured others. It says two Kenyan troops were injured in the clash, one critically. The soldiers were airlifted out for medical treatment.

The statement also said Kenyan forces conducted an airstrike on an al-Shabab training camp , have captured the town of Busar and are advancing on two other towns.

There was no immediate comment from al-Shabab.

Kenya sent forces into southern Somalia this month to weaken al-Shabab, who officials blame for the cross-border kidnapping of several foreigners.

Thursday's statement says Kenya's goal is to reduce al-Shabab effectiveness and to restore the Somali government's authority in al-Shabab controlled areas.

The militant group, which controls large portions of southern and central Somalia, is trying to topple the Somali government and set up an Islamic state. It has denied playing any role in the kidnappings.

Earlier, at least four Kenyan government workers were killed when their vehicle was hit by a rocket-propelled grenade in northeastern Kenya in an area not far from the Kenyan-Somali border. It was not immediately clear who was behind the attack.

The incident is the latest in a series of attacks across the country, following a warning from al-Shabab that it would attack targets in Kenya in response to the Kenyan incursion.

On Wednesday, a Kenyan man who admitted to being a member of al-Shabab, pleaded guilty to one of two grenade attacks that took place in Nairobi earlier this week. The explosions killed one person and injured more than 20 others.

Somalia's president and prime minister issued opposing statements on whether the Kenyans are welcome in their country. The prime minister came out in favor of the incursion in an interview with VOA ((Somali Service) Wednesday, while the president has said only African Union troops can operate legally in Somalia.