Kenya's army said on Saturday that four months of military strikes on Shebab rebels in southern Somalia have weakened the Al-Qaeda-linked insurgents and have disrupted their sources of revenue.

Air strikes and ground raids had cut off Shebab's trade routes and drove them from key towns where they conducted business, said military information and operations officer Colonel Cyrus Oguna.

"Al-Shebab is considerably weakened," Oguna told reporters. "In terms of revenue that Al-Shebab is earning, it is totally disrupted. In our own assessment, 75 percent of revenue collection of Al-Shebab has been disrupted."

Kenya sent forces into southern Somalia last October to fight Shebab following a series of cross-border attacks and kidnapping of foreigners that Nairobi blamed on the insurgents.

In retaliation, the Shebab have carried out grenade attacks and abductions in areas near the porous Kenya-Somalia border, killing and wounding several people.

Oguna said several local Shebab commanders were killed in a raid this week in a southern Somalia town and that the rebels have lost several towns in the battle.

"When a force is losing revenue collection and also losing command elements, what that means is that the capacity of that force to fight is completely reduced," Oguna said.

The Shebab have been facing increasing encirclement by regional forces. In addition to Kenya, Ethiopia deployed troops in western Somalia.

In Mogadishu where the Shebab abandoned fixed bases in August, a 10,000-strong African Union force comprising Burundi, Djibouti and Uganda troops is battling the remaining rebels.

The rebels however still control large areas in the south of the conflict-torn Horn of Africa country.