Uncharged phones and laptops will be barred from planes going to the US under new security measures, the US Transportation Security Administration (TSA) said.
The new rules come amid growing concern about the increased capability of al-Qaeda affiliates in Yemen and Syria, and the threat the foreign fighters of Syria pose to the home countries.
Officials in the US say some passengers at overseas airports will be asked to turn on their phones under new security measures.
The Transportation Security Administration (TSA) said it will require some foreign airports to order passengers to turn on devices such as mobile phones. Any that do not power up will not be allowed on flights to the US, and those travellers may have to undergo additional screening.
The latest security measures imposed last week followed intelligence warnings that al Qaeda's chief bomb maker, Ibrahim Hassan al-Asiri, who is thought to be based in Yemen, had linked up with jihadists in Syria to pass on his skills.
I have no doubt, from what I have learnt, that these new steps are not bureaucratic nor an overreaction.
Sadly, they are unavoidable.
It is simply foolish to believe that the threat is either minimal or now behind us.
We have, indeed, been fortunate but, sadly, this has not been because the terrorists have, since 2005, given up trying to do us harm.
As Andrew Parker, the head of MI5, has made clear, each year there have been serious plots which if they had not been identified and disrupted would have led to the deaths and mutilation of many British citizens.
Sir Malcolm Rifkind, the chairman of the Intelligence and Security Committee, who disclosed that he had been briefed in advance about the measures, said that he had been left in no doubt that they were necessary.
However, he said that he had encountered a level of complacency among some elements of the public which he found "seriously disturbing".
The head of the parliamentary committee which oversees the work of Britain's intelligence agencies has said that newly imposed airport security measures are "unavoidable".
Sir Malcolm Rifkind, the chairman of the Intelligence and Security Committee, said jihadi extremists were deploying "devilish technical skill" to create ever more sophisticated devices to evade existing security measures.
Writing in The Sunday Telegraph, he warned of the dangers of "complacency" among the public in the face of the failure of the terrorists to mount any successful mass casualty attack in the UK since the 7/7 bombings in London in 2005.
The three heads of the UK's Intelligence Agencies will make history this afternoon when they appear in public together for the first time to talk about their work.
GCHQ director Sir Iain Lobban will join Andrew Parker, the director general of the Security Service and Sir John Sawers, chief of the Secret Intelligence Service at the Intelligence and Security Committee's first open evidence session.
The televised proceedings will be subjected to a two-minute delay to prevent anything that might endanger national security or the safety of those working for the agencies being broadcast.
A criminal investigation has been launched into a contract between security firm G4S and the Government for tagging criminals.
An inquiry has been opened by the Serious Fraud Office after it emerged G4S, along with Serco, had charged the Ministry of Justice for monitoring offenders who were dead, back in prison, had their tags removed, left the country or never been tagged in the first place.
An audit by accountancy firm PricewaterhouseCoopers, launched in May, alleged that overcharging began at least as far back as the start of the current contracts in 2005.
The Government reported G4S in July when the FTSE 100 firm refused to take part in an additional audit to rule out any dishonesty.
The United Nations is to contact the United States about reports that America's National Security Agency hacked the world body's internal communications, according to the Associated Press agency.
The UN emphasised that international treaties protected its offices and all diplomatic missions from interference, spying and eavesdropping.
Its spokesman Farhan Haq said the UN would "reach out" to US officials about the reports of eavesdropping, as it has in the past when such allegations have been raised.
Former Labour Home Secretary Jack Straw criticised Deputy Prime Minister Nick Clegg's stance against increasing internet monitoring powers for security services.
He told BBC2's Newsnight: "He needs to think about what is more important: supporting Google and Amazon and these other American behemoths; or supporting security and reassurance for the British people."
Mr Clegg blocked the Communications Data Bill as he said it was "disproportionate" and in his view "unworkable".
There have been calls for the Communications Data Bill, dubbed the "snoopers charters" to be revived in the wake of the terror attack on Drummer Lee Rigby.
The bill was previously blocked from the Queen's Speech by the Deputy Prime Minister Nick Clegg who has said it had "proved to be either disproportionate in my view or not workable".
Four home secretaries are among senior politicians who have written a letter in The Times calling for security services to be given increased internet monitoring powers.
Labour's Jack Straw, David Blunkett and Alan Johnson, and Conservative Lord Baker signed the letter which says:
Coalition niceties and party politics must not get in the way of giving our security services the capabilities they need to stay one step ahead of those that seek to destroy our society.
When such a threat reveals itself, government has a duty to ensure they can do all they can to counter it.
Far from being a 'snoopers' charter', as critics allege, the draft bill, seeks to match our crime fighting capabilities to the advances in technologies.
The proposed Communications Data Bill does not want access to the content of our communications but does want to ensure that enough data is available in the aftermath of an attack to help investigators establish 'who, where and when' were involved in planning or supporting it."
Tory former defence secretary Lord King, and Liberal Democrat Lord Carlile, the former independent reviewer of UK anti-terror laws, also added their signatures.