British police arrested a man at London's Gatwick Airport Thursday with a grenade in his luggage, and two other suspects were taken into custody near Heathrow Airport, where troops have been on patrol after a terrorist threat.

Metropolitan Police said a 37-year-old Venezuelan national was arrested at London's Gatwick when officers found the grenade, which appeared to be live, in his baggage after he arrived on a British Airways flight from Colombia.

Officers evacuated part of the airport after the discovery and suspended flights from its North Terminal at 2 p.m. A spokeswoman for the airport said all passenger areas in the North Terminal were closed and police were present.

Police said the flight, British Airways 2048, originated in Bogota, and stopped at the Caribbean island of Barbados. The suspect boarded in Bogota, police said.

A Home Office spokesman said police did not yet know the man's intentions.

"It is not uncommon for people in airports to be discovered with some form of weaponry," the spokesman said on condition of anonymity. "It doesn't mean they are all Al Qaeda terrorists."

"People should not jump to conclusions about this incident and should give police time to assess whether this was anything more than a lone individual carrying something he shouldn't have been."

Police said they had arrested two men in Hounslow, just east of Heathrow airport. They were being held at a police station in west London. Police did not say what led to those arrests.

In Parliament, lawmakers pressed the government to say more about the threat that led to the intensified security, but Prime Minister Tony Blair ruled out a full explanation.

"We cannot start disclosing details of everything we know or may know," Blair told a news conference. "But it's important we take every precaution we can in order to keep people safe."

Britain has deployed hundreds of soldiers at Heathrow, Europe's busiest airport, over the last three days after police warned that the Al Qaeda network might try attacking London during this week's Muslim festival of Eid al-Adha.

Home Secretary David Blunkett said Thursday that Usama bin Laden's Al Qaeda network was a threat, but added he was withholding specifics to protect security sources.

"We know that Al Qaeda will try to inflict loss of human life and damage on the United Kingdom," Blunkett told lawmakers in the House of Commons, adding: "The terrorists must not be able to assess what we know and how we know it."

The Ministry of Defense said a Nimrod surveillance plane was flying over the London area, but added that fighter jets were not being used. Police have boosted security in the center of the capital and at Manchester airport in northern England.

Light tanks deployed at Heathrow for the last two days were not in evidence Thursday, but there seemed to be more spot checks of automobiles near the airport, Associated Press photographer Max Nash said. In one village along the flight path west of Heathrow, police were stopping nearly every car, Nash said.

The Guardian newspaper reported Thursday that the security alert was sparked by "high-quality" intelligence that Islamic extremists had smuggled Sam-7 anti-aircraft missiles into Britain from Europe. Police refused to comment on the report, which said the intelligence was the most specific information of an imminent threat since the Sept. 11 attacks.