Kenya says its fighter aircraft will destroy weapons flown into Somalia for the Al Shabab group.
Kenya sent troops into Somalia in mid-October to fight Al Shabab, which it it blames for a recent spate of kidnappings.
The Kenyan army says two planes landed in Baidoa with weapons and ammunition for al-Shabab. It did not specify where the aircraft had come from.
Major Emmanuel Chirchir warned that air strikes against al-Shabab targets were imminent to prevent the weapons reaching fighter bases.
He advised civilians in 10 towns to stay away from al-Shabab camps.
Major Chirchir said an earlier aerial bombardment of Jilib on Sunday by a Kenyan fighter jet hit al-Shabab positions, killing 10 militia fighters.
But MSF-Holland, a medical charity, said at least five people died after a camp for displaced people was bombed.
The BBC reports people abducted from Kenya since September include a French woman; a British woman taken from a coastal resort; and a Kenyan driver and two Spanish aid workers seized from the Dadaab refugee camp.
Meanwhile there are conflicting accounts of losses following a battle involving Kenya, Somali government forces and al-Shabab on Tuesday.
al-Shabab said seven Kenyan soldiers were killed and two armoured vehicles destroyed during an ambush - which Kenya denies.
The BBC's East Africa correspondent reports it's hard to know who's telling the truth in the propaganda war.