A suicide attack on a hotel near Mombasa killed 15
There is shock in Kenya at the decision by the UK Government to ban British commercial flights to and from Nairobi indefinitely.
Speaking at Kenya's main airport, the country's permanent secretary in charge of national security, Dave Mwangi, said they were "very, very surprised" at the UK decision.
It was taken without consulting the Kenyan Government and was unjustified, he told the BBC's Network Africa programme.
"We believe they are acting out of panic for no reason at all," he said.
On Friday the UK Foreign Office also warned of a "clear terrorist threat" in six other East African countries: Djibouti, Eritrea, Ethiopia, Somalia, Tanzania and Uganda.
It did not advise UK citizens to avoid all non-essential travel there - unlike the advisory about Kenya. But it did urge them to be vigilant, especially in places frequented by foreigners.
The US Government also warned Americans to postpone non-essential trips to Kenya.
The UK's flight ban came into force a day after Kenyan security forces said they believed a leading al-Qaeda suspect, named as Fazul Abdullah Mohammed, had returned to Kenya.
He is accused by the FBI of involvement in the bombing of American embassies in East Africa in 1998.
The UK Government said they believed the threat of an attack on British citizens was high.
But Mr Mwangi denied the Kenyan Government warning had suggested that.
"We were only cautioning Kenyans and those who live in Kenya that our security forces are alert," he said.
"If anyone tries to come in for any acts of terrorism we are ready and waiting."
"We are very well equipped to detect any trouble. We now have an anti-terrorist unit that is very active and will ensure we are safer than other countries around the region here," he told the BBC.
Some criticism of how the Kenyan Government has handled the latest terror threat is emerging.
Security Minister Chris Murungaru had placed the country's security forces on high alert on Wednesday, but said he did not speak of any specific threat to Kenya.
But Mohammed Sheikh, an Islamic scholar in the Kenyan coastal resort city of Mombasa, told the BBC that he had not handled the latest warning correctly.
"It's unfortunate that the minister had to issue the statement the way he did. He could have done it much more quietly. He went about it the wrong way."
The UK flight ban is a major blow to Kenya's struggling tourism industry, already reeling from an attack on an Israeli owned hotel and a failed attempt to shoot down a plane in Mombasa in November last year.
About 100,000 Britons holiday each year in Kenya, although less than 2,000 are believed to be in the country at present, as it is in the middle of the rainy season.
The Foreign Office has advised Britons already in Kenya to keep a low profile and to be very vigilant in public places.
Kenya Airways is still flying between the UK and Kenya, but other Western airlines are said to be considering their position.
Tourism Minister Raphael Tuju told Reuters news agency: "My personal reaction is that I would rather have flights cancelled than one person die."