Kenya is worried the lawlessness in Somalia could spill over the border
Kenya has promised to reinforce its border with Somalia after several abductions near the frontier.
Officials have been discussing how to stop incursions since the weekend, when militants snatched three foreign aid workers from the town of Mandera.
A defence spokesman promised to try to stop the militants, but said it was often difficult to identify them.
Meanwhile, Kenyan President Mwai Kibaki blamed Somali insurgents for an influx of illegal weapons into his country.
Defence spokesman Bogita Ongeri said his forces were working with other nations to try to keep Somali militias such as the radical al-Shabab group at bay.
"The challenge that we have at border points is that these people come from the same clan, and you find that sometimes to identify who is al-Shabab and who is not is a problem," he said.
"Our borders are porous and it is not a place where you can totally keep al-Shabab at bay. But we are trying our best."
The BBC's Ruth Nesoba, in Nairobi, says a series of incidents on the Somali border has raised questions about the ability of Kenyan security agents to keep the country safe.
On Saturday alleged members of al-Shabab crossed into Kenya, kidnapped three aid workers in Mandera and returned to Somalia - apparently without any resistance.
Our correspondent says the incident came just days after militants were reportedly sighted trying to recruit young men outside a local school on the Kenyan side of the border.
During a speech to the armed forces, President Kibaki linked the insurgency in Somalia to the rise of insecurity and crime in his country.
"The continued fighting in neighbouring Somalia has contributed immensely to the infiltration of these illicit arms into our country," he said.
"My government will not spare any efforts to mop up illicit arms that are used by criminals to carry out banditry attacks."
Earlier this year militants from Somalia abducted two Italians nuns from the same border area.
The two were released a few weeks later after ransom money was paid.