Nairobi, Kenya (CNN) -- Islamic militants have moved fighters to the Somali border town of Afmado in an effort to combat Kenyan forces who have entered Somalia, the militant group Al-Shabaab said Tuesday.
The group said it viewed the Kenyan forces crossing of the joint border as "an affront to Somalia's territorial sovereignty."
This move of fighters, which started Monday, comes after the militant group had threatened to "come into Kenya" if Kenyan forces did not leave Somalia.
"Kenyan troops have entered 100 kilometers into Somalia, and their planes are bombarding and killing residents," Sheikh Ali Mahmud Ragi, spokesman for Al-Shabaab, said in an online message posted on a jihadist website this week. "We shall come into Kenya if you do not go back."
In response, the Kenyan and Somali governments issued a joint communique declaring Al-Shabaab "a common enemy to both countries." They pledged to work together to stabilize Somalia and cooperate in security and military operations.
Kenyan forces crossed into Somalia to pursue Al-Shabaab fighters after the recent abductions of tourists and aid workers in Kenya heightened tensions in East Africa. Kenya invoked the U.N. charter allowing military action in self-defense against its largely lawless neighbor.
The abductions are part of a "recent spate of blatant attacks" that are part of "a changed strategy by Al-Shabaab calculated to terrorize civilians," the communique said.
"If you are attacked by an enemy, you have to pursue that enemy through hot pursuit and to try (to) hit wherever that enemy is," said Kenyan Defense Minister Yusuf Haji in a news conference that aired Sunday on CNN affiliate NTV.
Al-Shabaab, which is linked to al Qaeda, has been fighting to impose its interpretation of Islamic law, or sharia, on Somalia. The group issued a statement Tuesday, however, denying responsibility for the abductions.
"These are mere suppositions unfounded in any solid evidence," the statement said. "Kenyan authorities have been seeking justification for an aggressive incursion on to Somali territory."
On September 11, armed bandits broke into a beachfront cottage where Britons Judith and David Tebbutt, both in their 50s, were staying. David Tebbutt was shot dead while trying to resist the attack. His wife was grabbed and spirited away on a speedboat, and is believed to have been taken into Somalia.
On October 1, pirates made another cross-border raid, this time snatching a French woman in her 60s from a holiday home on Manda Island where she lived part of the year.
Earlier this month, gunmen abducted two Spanish workers from the medical charity Doctors Without Borders from the Dadaab refugee complex, about 80 kilometers (about 50 miles) from the Somali border.
Kenya announced its new tactics days after African Union forces claimed victory against Al-Shabaab in the Somali capital of Mogadishu. The military said last week it had taken the remaining Al-Shabaab strongholds in the far northeast of the city.
"The challenge is now to protect civilians from the sort of terror attack we saw last week, as they attempt to rebuild their lives," said Lt. Col. Paddy Ankunda, spokesman for the African Union Mission in Somalia. He was referring to a suicide truck bombing in Mogadishu this month that left dozens dead. Al-Shabaab claimed responsibility. Other Al-Shabaab attacks that week led to the deaths of at least 10 civilians.
Federal and African Union forces have battled Al-Shabaab in the impoverished and chaotic nation for years. Many analysts believe the military push has severely affected Al-Shabaab, along with targeted strikes against organization members and the weakening of al Qaeda.
Al-Shabaab said in August it was withdrawing from Mogadishu, and Somalia's Transitional Federal Government, backed by African Union peacekeepers, now controls most districts of the capital, the U.N. office has said.
However, the group still poses a threat, Ankunda has said.