Tensions between the Kenyan government and the al-Shabab militants who control much of neighboring Somalia have ramped up following reports that Kenyan soldiers have crossed into Somali territory to search for kidnappers who seized two westerners.

Over the weekend, Kenya launched ground and air troops into Somali following a spate of abductions, most recent of which was the kidnapping of two female Spanish aid workers who were treating refugees who had fled to Kenya. Over the past month, two more westerners (both women) have been abducted and spirited off to Somalia.

Our territorial integrity is threatened with serious security threats of terrorism. We cannot allow this to happen at all, Kenya's Internal Security Minister George Saitoti told reporters.

It means we are now going to pursue the enemy, who are the al-Shabab, to wherever they will be, even in their country.

Kenyan officials blame the abductions on al-Shabab, an Islamist group that controls large swathes of Somalia and are linked to al-Qaeda. Al-Shabab is concurrently involved in a deadly struggle against the United Nations-backed transition government which controls only the capital city of Mogadishu.

In response, al-Shabab has issued a warning against Kenya to withdraw its troops or risk violence.

Ali Mohamud Rage, a spokesman for the Somali militants, told BBC that his fighters would attack Nairobi, the Kenyan capital, in retaliation. For the record, al-Shabab has also denied it abducted the westerners.

We will defend ourselves,” Rage said. “Kenya doesn't know war. We know war. The tall buildings in Nairobi will be destroyed. We have fought against governments older and stronger than Kenya and we have defeated them.

Reportedly, hundreds of al-Shabab fighters have amassed at a location where they believe Kenyan forces that crossed into.

However, no battles or confrontations have been reported.

A Kenyan officer told Reuters: Our team inside Somalia is doing well. So far, we have uprooted al-Shabab from [the district of] Dhobley after air and ground raids. We are working with other friendly armed groups... to fight the common enemy, al-Shabab.

Indeed, Moses Masika Wetangula, Kenya’s foreign minister claims that Somalia's transitional government invited Kenyan troops into their country.

What we are doing is in pursuit of a request by the government of Somalia and also our own interest as a country to fight a group that is terror-based, he told BBC.

However, this view is apparently not widely believed.

BBC correspondent in Nairobi, Kenya, Will Ross wrote: “Eyewitness reports say there is a heavy military presence of Kenyan personnel inside Somalia, including air power. From the [legitimate] Somali government's point of view it will want to send out a message that it can cope with things on its own, that it does not want more foreign troops in Somalia -- there are already Ugandan and Burundian propping up the government in Mogadishu -- so it is a bit embarrassing to then have another country coming in to help out.”

Ross added: “From the Kenyan point of view it is trying to send out a message that it is very serious about security -- the Kenyan government says it is going after al-Shabab because it thinks the group was behind the recent kidnappings. It is a message aimed at the Kenyan population to say 'look, we can still fight, we can still defend our country'.”

However, al-Shabab has rarely acted beyond Somali’s borders. In 2010, it reportedly committed a suicide bombing in Kampala, Uganda which killed dozens of people.

These [al-Shabab] are criminals, and it's important to indicate we are not at war with the government of Somalia, or with the people of Somalia, Francis Kimemia, permanent secretary at Kenya’s Ministry of Internal Security, told privately-owned Citizen Television.

Reportedly worries are growing that the incursion into Al-Shabab territory will make Kenya a target for terrorist acts in the near future.

Complicating matters greatly is the hundreds of thousands of Somali refugees who have poured into Kenya in recent months to escape al-Shabab, drought and famine.