US officials believe terrorists in Syria and Yemen could be developing explosives that could be smuggled on to planes

A tightening of security at UK airports may remain in place on a permanent basis in the face of a new extremist bomb threat to transatlantic aircraft, Nick Clegg has said as he warned of the dangers posed by a "medieval, violent, revolting ideology".

Speaking after the government announced an increase in airport security amid fears in the US that terrorists in Syria and Yemen were developing explosives that could be smuggled on to planes, the deputy prime minister said the new measures would not be temporary.

"I don't think we should expect this to be a one-off temporary thing," Clegg said on his weekly LBC phone-in. "We have to make sure the checks are there to meet the nature of the new kinds of threats. Whether it is forever – I can't make any predictions. But I don't want people to think that this is just a sort of a blip for a week. This is part of an evolving and constant review about whether the checks keep up with the nature of the threats we face."

Clegg was speaking after US officials told Reuters that security at European airports would be increased following intelligence that al-Qaida operatives in Syria and Yemen had joined forces to develop bombs that could avoid detection and bring down aircraft. The US did not specify which airports or countries would be affected, nor did it say what triggered the extra precautions.

The warning from the US prompted the Department for Transport in Britain to announce a tightening of security at UK airports. It is thought that the extra measures at UK airports could include increased random screening of passengers and tighter scrutiny of footwear, mobile phones and computers. A DfT spokesman said the changes would not cause significant disruption to passengers and the threat level remained at substantial, meaning an attack was a strong possibility.

Clegg acknowledged that passengers would face disruption although he said there was no need for panic. He said on his weekly LBC phone-in: "It will involve extra checks of various descriptions. The checks we have in terms of passengers who go on aeroplanes, how they are scrutinised, how they are checked is – in the jargon – multi-layered. So there is going to be another layer for some travellers on some flights. I don't think people should be unduly panicked or concerned. But this is the world we now live in. This won't be the last time that there are further adjustments made because we are having to constantly evolve our own defences in view of the evolving way people want to attack us."

The announcement from the US of the need for increased security followed intelligence reports which suggested that bombmakers from Yemen-based al-Qaida in the Arabian peninsula (AQAP) have travelled to Syria to meet al-Qaida-affiliated Jabhat al-Nusra to work on ways to get an explosive device past existing security.

Clegg said the world needed to accept that it was facing a major threat from forces distorting Islam, as he highlighted the declaration by the Islamic State of Iraq and the Levant (Isis) of a caliphate. Isis is in dispute with Jabhat al-Nusra, which is thought to be behind the alleged bomb plot.

The deputy prime minister said: "What is going on in Syria – the establishment of this self-declared caliphate across the border of Syria and Iraq – is now the latest turn of the wheel in a really ugly, medieval ideology. We need to be really, really clear that they are basing their whole world view on a kind of medieval, violent, revolting ideology that, by the way, is a total and utter aberration and distortion of what the vast, vast, vast majority of the millions of Muslims around the world believe in. It is a grotesque distortion of that faith."

The US department of homeland security said enhanced security measures would be implemented in the next few days at "certain overseas airports with direct flights into the United States".

The department secretary, Jeh Johnson, said: "We are sharing recent and relevant information with our foreign allies and are consulting the aviation industry."

US intelligence agencies believe extremists in Syria and Yemen have been in contact to develop bombs that escape heightened security measures, although they do not have specific intelligence about an imminent attack or specific plot emanating from the suspected collaboration.

Some in the US intelligence community also believe that training complexes have been set up in Syria for western jihadists so they can return to their home countries better trained to carry out attacks.

While that conclusion is the subject of debate, it shows the level of fear counter-terrorism officials have about the threat posed by jihadists from Syria – now considered to be the main threat facing the west.