Members of the Queen's Royal Guards had been removed from high-profile public posts outside key royal residences in London in view of the escalated security threats, Mashable reported.
This was the first time since the height of the IRA's campaign in the 1980s that the guards were no longer allowed on sentry duty alone.
According to media reports, the guards had been moved away from tourists and were now behind metal gates with some accompanied by armed policemen. The Mirror reported that in internet chatter picked up by intelligence services an ISIS plot similar to the "lone wolf" attack on fusilier Lee Rigby had been mentioned.
In May 2013, two attackers drove a car into Rigby and later brutally hacked him to death in Artillery Place, Woolwich, south-east London.
The Queen's Guards are tasked with guarding the official royal residences - Buckingham Palace, St James's Palace, Windsor Palace, the Tower of London and the Palace of Holyroodhouse in Edinburgh.
Though they are mostly known for ceremonial duties and for being tourist attractions, the Queen's Guards, also serve as soldiers with the armed forces.
Meanwhile, Mail Online reported that the soldiers had been moved behind metal fences because of fears of a terror attack, local newspapers reported today.
The soldiers had been separated from the public, with armed police providing additional protection.
According to The Telegraph newspaper, Buckingham Palace and the police feared that militant Islamists could see the Royal Guards as high-profile targets. Although the guards carried weapons fitted with bayonets the guns were not loaded.
The UK raised its terrorism alert to the second-highest level in August and last month said it faced the biggest terrorism threat in its history due to radicalised UK citizens returning from fighting in Syria and Iraq.
Earlier this month the UK's top policeman said the country had thwarted a 'lone wolf' style attack only days before it was due to happen, and that five terror plots had been foiled by authorities in the last four months.
Two months back a man shot dead a soldier on ceremonial sentry duty in the Canadian capital Ottawa. The man later charged into the parliament building.