Kenya's military warned the residents of 10 towns in Somalia on Tuesday, including the port city of Kismayu, Baidoa and Afgoye near the capital Mogadishu, that they will be under attack continuously.
The fact the towns listed include places well beyond the southern part of Somalia where Kenyan troops are advancing suggests that Kenya may step up airstrikes on other areas where al Shabaab insurgents have strongholds.
Somalia's al Shabaab rebels also ambushed a Kenyan military convoy in the south of the Horn of Africa nation on Tuesday, the insurgents, a militia fighting with Kenyan and Somali government troops and a Kenyan security source told Reuters.
Kenya sent troops into Somalia in mid-October in pursuit of the al Qaeda-linked militants it blames for a series of kidnappings on Kenyan soil and frequent assaults on its security forces along its northern border with Somalia.
All three sources told Reuters the ambush happened on the road leading from the Kenyan border town of Liboi towards forward Kenyan troop positions further inside Somalia.
Kenyan troops were attacked on the same road last Thursday in the first serious clash with al Shabaab fighters since pushing into Somalia. Kenya's military said it killed nine al Shabaab fighters then and one Kenyan soldier died from his wounds.
A Kenyan security source, who declined to be named, said three of its soldiers were wounded in Tuesday's attack. Mahmud Farah, a spokesman for the pro-Somali government Ras Kamboni militia said no Kenyan soldiers died in the attack.
Sheikh Abdiasis Abu Musab, spokesman for al Shabaab's fighters, said they ambushed a Kenyan military convoy between Tabda and Dhobley and killed 10 soldiers.
Kenyan military spokesman Emmanuel Chirchir did not answer phone calls from Reuters seeking comment about the attack or the warning issued on his Twitter account.
Chirchir said on Twitter that anyone with relatives and friends in the 10 Somali towns listed as targets by the Kenyan Defence Forces should be advised accordingly.
The main objective of Kenyan ground forces is to seize the southern port of Kismayu, as this is a key al Shabaab stronghold and an important source of funding for the al Qaeda-linked militants, and to dismantle the rebel network.
Operation Linda Nchi is on course, advance to Kismayu is on schedule, Chirchir said.
The Kenyan operation is called Linda Nchi, which means Protect the Nation in the Swahili language.
Other towns listed by the Kenyan Defence Forces spokesman included Buale, Afmadow, Baar Dheere, Dinsoor and Jilib, the place hit by a Kenyan airstrike on Sunday.
Chirchir said the Kenyan military had received reliable confirmation that two aircraft had landed in the town of Baidoa with a consignment of arms destined for al Shabaab.
Baidoa, about 270 km northwest of Mogadishu, used to host Somalia's parliament, before the rebels seized it in early 2009.
(Additional reporting by Feisal Omar in Mogadishu, David Clarke and Sahra Abdi in Nairobi; Editing by Richard Lough)