Kenyan forces will pursue gunmen accused of a spate of kidnappings of foreigners across the two nations' border, the internal security minister said Saturday.

Branding Somalia's Al-Qaeda inspired Al-Shebab rebels "the enemy", George Saitoti said Kenya intended to track down the kidnappers whose raids on two beach resorts have dealt a major blow to Kenya's tourism industry.

"Our territorial integrity is threatened with serious security threats of terrorism, we cannot allow this to happen at all," said Saitoti.

"It means we are now going to pursue the enemy, who are the Al-Shebab, to wherever they will be, even in their country," he told reporters.

In just over the past month, a British woman and a French woman have been abducted from beach resorts, while two Spanish aid workers were on Thursday seized from a refugee camp.

Police have blamed the abductions on the Islamist Shebab, but experts say the kidnappings could also be the work of pirates, bandits or opportunistic criminal gangs.

"If you are attacked by an enemy, you are allowed to pursue that enemy until where you get him," said Kenyan Defence Minister Yusuf Mohammed Haji, speaking alongside Saitoti. "We will force them far away from our border."

Security forces were still searching Saturday for the two Spaniards, both logistics officers with the aid group Medecins Sans Frontieres (MSF, Doctors Without Borders), who were abducted from Kenya's Dadaab refugee camp and are believed to have been taken over the border.

"The militants are still being pursued," Saitoti said. "We have mobilised adequate security forces who are still pursuing them."

Large numbers of Kenyan security forces including helicopters were reported close to the Somali frontier on Saturday, an AFP reporter in the area said.

Kenyan military vehicles were seen driving through scrubland near the Liboi border post.

"Everything possible is being done to ensure those kidnapped are found," Haji added.

Kenya is still reeling from the kidnapping of the French and British women from coastal regions which has badly damaged its key tourism sector.

Aid agencies said they were halting all but life-saving relief efforts in Dadaab -- the world's largest refugee camp, and home to some 450,000 mainly Somali refugees fleeing drought, famine or war -- as they reviewed security.

Kenyan authorities have on several occasions expressed fears Islamist extremists would infiltrate the Dadaab camps from Somalia, as the border lies barely 100 kilometres (60 miles) away.

Kenya also said it had shut its border with Somalia, although enforcing that move across the porous frontier will be a near impossible move in reality.

"We have closed the border with Somalia and we have no apology to make," Saitoti said, adding that security officials would search all refugees entering and already in Kenya, claiming not all were "a bona fide refugee".

The Dadaab camp complex has seen a huge influx of people this year -- over 7,500 people have arrived in the crowded complex of rag, tin and plastic huts this month alone.

The exodus has been sparked by a severe drought that has affected more than 13 million people across the Horn of Africa, hitting Somalia especially hard.

"Why is it that this refugee issue is being seen as a Kenyan issue?" Saitoti added.

"We want the international community to stabilise Somalia so that these refugees can be taken back there," he said.

Somalia has had no effective government ever since it plunged into repeated rounds of civil wars beginning in 1991, allowing a flourishing of militia armies, extremist rebels and piracy.

The Shebab have reportedly denied involvement in the kidnappings, according to the World Health Organisation's representative for Somalia.