Updated

MOGADISHU, Somalia-- Somalia's most dangerous militant group threatened Kenya with suicide attacks on Monday, saying Nairobi's skyscrapers would be destroyed and its tourism industry ruined in an ominous warning one day after Kenyan troops poured into Somalia.

Al-Shabab spokesman Ali Mohamud Rage told a news conference in Mogadishu on Monday that Kenya must pull its troops out of Somalia. "Otherwise remember what happened in Uganda's capital," he said.

Al-Shabab unleashed near simultaneous suicide bombings at public venues in Kampala in July 2010 as crowds gathered to watch the World Cup final on TV, killing 76 people. The militant group said the attack was in retaliation for Uganda's deployment of troops to Mogadishu as part of the African Union peacekeeping force there.

Hundreds of Kenyan troops poured into Somalia over the weekend following the kidnappings of four Europeans inside Kenya near the Somali border. Kenyan officials say the country has the right to defend itself from Somalia's most powerful militant group, though Rage denied the group had anything to do with the kidnappings.

"We say to Kenya: Did you consider the consequences of the invasion? We know fighting more than you and defeated other invaders before," Rage said.

"Your attack to us means your skyscrapers will be destroyed, your tourism will disappear. We shall inflict on you the same damage you inflicted on us. You have to see what happened to the other aggressors, like (Uganda President Yoweri) Museveni and his country when they invaded us. We hit them in their country," Rage said.

Rage said that Kenyan troops had pushed 60 miles (100 kilometers) across the Kenya-Somalia border.

A Kenyan military spokesman, Maj. Emmanuel Chirchir, declined Monday to say how many Kenyan troops have moved into Somalia. "We have sufficient forces," he said.

Chirchir said that five Kenyan troops died when a helicopter crashed in a Kenyan town near the border late Sunday. The deaths were the first confirmed casualties of the military push.
Residents in Somalia say fighter jets and helicopters have been flying overhead since the weekend.

Witnesses in the Somali town of Dhobley on Monday said an estimated 40 Kenyan military vehicles entered the town on Sunday. Ali Abdullahi, a resident in Dhobley, said the army vehicles were towing what he described as "big guns."

No large-scale fighting has yet broken out, the residents said.

Kenyan officials on Saturday said they would send troops into Somalia. That declaration came two days after armed militants kidnapped two Spanish aid workers with the group Doctors Without Borders from the Dadaab refugee camp in northeast Kenya, a sprawling expanse of temporary homes where almost 500,000 Somalis live.

On Oct. 1, Somali gunmen took a wheelchair-bound Frenchwoman from her home near the resort town of Lamu. Somalis also abducted a British woman from a Kenyan coastal resort in September. Her husband was killed in the attack.

Kenya's push east into Somalia will open another front that Somali militants must contend with. African Union forces from Uganda and Burundi have expanded their control of Mogadishu in recent months and have almost completely forced al-Shabab out of the capital.