British authorities have arrested four men on Tuesday suspected of planning to commit acts of terrorism in the city.

London's Metropolitan Police said they arrested the men ages 20 and 21 across the city as part of "an ongoing investigation into Islamist related terrorism," CNN has learned.

"They have all been taken to police stations in central London and remain in custody," police said. Their identities have not been released.

Authorities did not specify the nature of the attacks the men are suspected of planning. But Con Coughlin, defense editor for The Telegraph newspaper, told Fox News that inside sources said the ISIS-linked jihadists were planning on beheading citizens on the streets of London.

Coughlin said he was informed the alleged plot would have taken place in the next few days.

"This is an ISIS plot," the editor told Fox News. "This is the first ISIS plot we've had on the streets of London."   

The foiled plot, if true, is reminiscent of a May 2013 murder where British soldier Lee Rigby was stabbed and nearly decapitated by two men in public. One attacker was sentenced to life in prison, and the other received 45 years.

The arrests come as Western governments are leading a crackdown against citizens suspected of planning to join ISIS, also known as ISIL, in Iraq and Syria. On Saturday, U.S. federal agents arrested an Illinois teenager at an airport before he fled the country to join the jihadists in Syria, according to a criminal complaint.

The U.K. also recently joined a U.S.-led coalition of air strikes against militant targets in Iraq.    

ISIS- the Islamic State of Iraq and Syria- has become an increasing global threat as they take over villages and slaughter innocents that do not adhere to the group's strict religious ideals, all in the name of establishing a caliphate, or Islamic state.