The US authorities are introducing tougher screening rules for passengers arriving by air from nations deemed to have links with terrorism.Reports say people flying from Nigeria, Pakistan, Syria, Iran, Sudan, Yemen and Cuba will have pat-down body searches and have carry-on baggage searched.President Barack Obama condemned lapses following the alleged Christmas Day bomb plot against a US plane.He promised "to act quickly to fix flaws" in the security system.The new security directives will come into effect on Monday.But hours after the new measures were announced, there was a security alert at Newark International Airport near New York City as a man entered a secure area without being screened.Terminal C was locked down and passengers were evacuated from the secure area, then re-screened. Flights from the terminal were grounded.Random checksThe Transportation Security Administration said in a statement that the new rules apply to passengers flying from or through countries on the US state department's "State Sponsors of Terrorism" list - Cuba, Iran, Sudan and Syria - and "other countries of interest".Nigeria and Yemen have been linked to the alleged failed Christmas Day plot.The main suspect is Nigerian, and Yemen-based militants have claimed the attack.The BBC's Jane O'Brien in Washington says it is unclear whether a pat-down could have detected the device carried by 23-year-old Nigerian accused Umar Farouk Abdulmutallab in his underwear.But Mr Obama has been under pressure to make visible security improvements, she says.As part of the new guidelines, passengers travelling from any other foreign country will also be checked at random.Earlier, UK Prime Minister Gordon Brown gave the go-ahead for full body scanners to be introduced at Britain's airports.The machines are expected to be installed at London's Heathrow Airport and other hubs within weeks.Also on Sunday, both the US and Britain closed their embassies in Yemen because of what officials say are continuing threats from al-Qaeda.'Determined'John Brennan, the US deputy national security adviser, said the group had "several hundred members" in Yemen and was posing an increasing threat there."This is something that we've known about for a while," he said. "We're determined to destroy al-Qaeda, whether it's in Pakistan, Afghanistan, or in Yemen."Mr Brennan added: "We know that they have been targeting our embassy, our embassy personnel."Last week an organisation called al-Qaeda in the Arabian Peninsula urged Muslims to help in "killing every crusader who works at their embassies or other places".In an internet statement, the group also said it was behind the alleged Christmas Day airliner bomb plot.On Saturday, President Obama said the organisation appeared to have trained Mr Abdulmutallab, who is being held in a US prison.The US mission in Sanaa was the target of an attack in September 2008, which was blamed on al-Qaeda, and in which 19 people died, including a young American woman.Also on Saturday, Gen David Petraeus, head of US military operations in the Middle East and Central Asia, visited Yemeni President Ali Abdallah Saleh to pledge US support for the fight with al-Qaeda.The visit came a day after the general announced that the US would more than double counter-terrorism aid to Yemen this year.Source: BBC