CCTV shows bombers approaching the Pearl Continental Hotel
Rescuers are searching for victims of a suicide bomb attack on a luxury hotel in the Pakistani city of Peshawar which killed at least 18 people.
Rescue teams are picking through the rubble of the Pearl Continental Hotel recovering bodies and looking for more people trapped in the debris.
The UN says two of its employees - one from Serbia and the other from the Philippines - are among the dead.
No-one has admitted the attack, but Pakistani officials blame the Taliban.
They say a series of bombings in the country are a response to an army offensive against militants in the north-west, centred on the Swat region.
The latest attack came as the Pakistani army carried out an offensive in the Bannu district bordering semi-autonomous North Waziristan.
Artillery and helicopter gunships have pounded positions held by the Janikhel tribe, which is accused of aiding the Taliban.
The BBC's Syed Shoaib Hasan in Islamabad says the Peshawar attack bore similarities to one on the Lahore police headquarters last month.
Jill McGivering, BBC News
The PC is a well-known landmark in Peshawar. Often used by foreigners but also by Pakistani officials and businessmen, it is known for good Western as well as local food and 5-star service. All factors which may have contributed to its becoming a target.
When I visited recently, there was a whole series of security checks. First of vehicles, as they drove in, past heavy concrete barriers. Then of people, screened by metal detectors and bag searches.
But suicide bombers and gunmen are hard to stop. There are clear echoes of the devastating assault on the Marriott Hotel in Islamabad last September.
Security in Peshawar has worsened dramatically in the last year. Many of those who can afford to move have taken their families to Islamabad or beyond - abandoning a city now becoming consumed by fear and violence.
Gunmen forced their way through a security barrier, firing at guards, before a van packed with explosives was driven through and detonated in the car park.
Police believe the bomb contained about 500kg of explosives.
The death toll rose to 18 with the discovery of three bodies early on Wednesday, our correspondent says. At least 60 people have been injured.
"The number of casualties could rise as we fear that some people are still trapped under the debris," police spokesman Abdul Ghafoor Afridi told AFP news agency.
"One portion of the hotel was totally destroyed. Three people including a manager of the hotel are missing and we fear they are under the debris."
The injured include a British man and a German national, Peshawar district co-ordination officer Sahibzada Anis said.
Pakistani Prime Minister Yusuf Raza Gilani swiftly condemned the attack, describing it as "shameful".
The UN named its two employees killed in the attack as Serbian national Aleksandar Vorkapic, of the refugee agency UNHCR, and Perseveranda So of the Philippines who worked for the children's agency Unicef.
Unicef said the bombing was "reprehensible and unacceptable" and said it was "greatly saddened" by the death of Perseveranda So.
"She was in Peshawar, a dangerous and difficult environment, helping implement programmes to assist girls in gaining access to the education they so desperately need. She will be greatly missed," the statement said.
UN Secretary-General Ban Ki-moon spoke of "a heinous terrorist attack which no cause can justify".
At least a dozen UN workers had been staying at the hotel before heading out to refugee camps in North West Frontier Province.
Peshawar, the main city in the north-west, is not far from the Swat valley, where the government's offensive against the Taliban has been concentrated.
Eyewitnesses told the BBC News website the blast could be seen up to 5km (3 miles) away. The blast left a large crater and parts of the hotel were destroyed.
An injured man, Jawad Chaudhry, said he had been in his room on the ground floor when he heard gunshots, then an explosion.
"The floor under my feet shook," he said. "I thought the roof was falling on me. I ran out. I saw everybody running in panic. There was blood and pieces of glass everywhere."
Musa Khan, a BBC News website reader in Peshawar, said he was far away when the blast happened but could tell it was "huge".
"I was in the university lawn with my friends," he said. "I saw the red light from there blowing and then I heard a huge sound."
PAKISTAN UNDER ATTACK
5 June: Mosque blast kills at least 38 in Upper Dir district
28 May: At least 10 die in separate attacks in Peshawar
27 May: Car and bomb attack kills at least 23 at Lahore police HQ
30 March: Lahore police buildings attacked - 23 people killed
3 March: Seven die in attack on Sri Lanka cricketers in Lahore
20 September 2008: Islamabad Marriott Hotel bomb kills 40
Correspondents say the Pearl Continental - usually just called the PC - runs a series of security checks, first of vehicles as they drive in past concrete barriers, then of people who are screened by metal detectors and bag searches.
Taliban leaders have promised revenge attacks on major Pakistani cities and claimed responsibility for the bombing in Lahore last month.
A suicide attack on the Islamabad Marriott hotel last September killed at least 53 people and injured more than 266.
In Bannu, officials say 70 militants have been killed in the action which started on Tuesday, but the figures cannot be verified.
Security officials say the Janikhel tribe refused to hand over militants involved in the kidnapping of students and teachers from a college last week who were later freed.
A curfew has been imposed in Bannu.
Analysts say North and South and North Waziristan are strongholds for al-Qaeda and the Taliban.
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