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 .
NEW : Kenyan and Somali governments pledging cooperation in Al-Shabaab fight . NEW : U.S. military says it has killed a top leader of the Islamic extremist group Al-Shabaab. The move of Kenyan troops comes after threats from Al-Shabaab to enter Kenya .