Four Kenyan soldiers were wounded in a firefight with Somalia's al Shabaab rebels overnight, the latest in a series of recent clashes, five weeks after Nairobi first sent soldiers into its neighbour.
Kenya, the region's biggest economy, sent troops into Somalia to rout the insurgents it blames for kidnappings of Western aid workers and tourists on Kenyan soil, and frequent cross-border incursions.
Al Shabaab has denied responsibility for the abductions.
After a fairly smooth advance, Kenya's forces fighting al Shabaab have since been camped near several rebel strongholds, but have yet to have a major showdown with the insurgents, nor seize any significant strategic bases.
The Kenyan army said on Saturday its progress had been hampered by heavy rain in an area with few tarmac roads, and because its troops were rooting out al Shabaab sympathisers in areas it now controls while feeding the famine-hit population.
It takes time. When we are done with that we will be able to move forward, said Colonel Cyrus Oguna.
He also said al Shabaab fighters had shifted their tactics to guerrilla-style warfare, using roadside bombs, grenade attacks and hit-and-run raids.
The clash overnight on Saturday was about 20 km (13 miles) inside Somalia from the border town of El Wak.
Kenyan military spokesman Emmanuel Chirchir said their forces and Somali government troops bumped into an al Shabaab camp while on patrol late at night.
He said in a statement that four Kenyan soldiers had been wounded, one critically, and nine al Shabaab fighters killed. He also said seven people had been arrested in a raid at El Wak and a number of weapons recovered.
There was no immediate comment from the rebels.
Oguna said on Saturday that Kenya had lost five soldiers since the start of the campaign and a couple had been wounded. He said several hundred al Shabaab fighters had been killed.
(Reporting by Noor Ali; Editing by David Clarke and Andrew Heavens)