There is little to stop terrorists behind the Moscow theatre attack joining the thousands of migrants crossing the US border and attempting something even bigger on American soil, officials have warned.
Isis-K, the jihadist splinter group which killed 143 in the March 23 massacre, regards the US as a 'bigger' target and 'could slip undetected' through America's 2,000 mile border with Mexico.
'The open border is a huge concern for terrorists entering the US in light of the attacks in Moscow,' a US counter-terrorism official told the NY Post.
'We are taking the threat of a domestic ISIS-K attack very seriously.
'They hate us, and everything we stand for. And they're bold and they're always looking for targets.'
Security footage recorded four Isis-K terrorists massacring 143 people at Moscow's Crocus City Theatre earlier this month in Europe's deadliest terror attack for 20 years
US security officials fear the terror group regards the US as a more attractive target and that there is little to stop it sneaking operatives into the thousands crossing the southern border
'It's only going to take a few of them to bring terrorism to US soil' said former Army intelligence officer Morgan Lerette
More than 2 million people were intercepted while crossing the southern border last year, but no one knows how many more came through unseen.
Meanwhile the number of intercepted migrants found to be on the FBI terror watch list has shot up from 15 in 2021, to 169 last year.
One of them, Lebanese migrant Basel Bassel Ebbadi, 22, told officials 'I'm going to try to make a bomb' after Border Patrol officials caught the Hezbollah member near El Paso in Texas earlier this month.
The Afghan-based Isis-K have already claimed American lives when they carried out a bomb attack that killed 183 people during the US evacuation of Kabul in 2021.
Daniel Byman of the Center for Strategic and International Studies said they are the 'most operationally capable off-shoot of the Islamic State' which seized control of large parts of Iraq and Syria between 2016 and 2018.
The group used nationals from Tajikistan for the Moscow attack, but Byman said they are actively recruiting in the other central Asian countries of Kazakhstan, Kyrgyzstan, Turkmenistan and Uzbekistan.
The FBI revealed last year that Isis-K has established a trafficking network to smuggle Uzbeki's into the US and that more than a dozen had disappeared after being processed by DHS officials.
FBI director Christopher Wray flagged the danger less than two weeks before the Moscow attack when he spoke to a Senate Intelligence Committee hearing earlier this month.
Wray replied 'I do' when asked by Cornyn about whether he is concerned if potential terrorists coming across the southern border could do harm to Americans earlier this month
The Tajik terrorists used automatic rifles, bombs and Molotov cocktails in their attack
Social media footage showed the gunmen dressed in camouflage clothing opening fire in the crowded Moscow theatre
The attack left the theatre in flames and Russian society facing an unprecedented terror threat
The FBI discovered an ISIS terrorist cell that used human trafficking operations to infiltrate the US but its members had disappeared by the time they realized
At least 7.2 million individuals have entered the US through the southern border since President Biden took office
Marco Rubio the vice chair of the committee said the briefing left him 'very concerned' about the potential threat.
'I think common sense tells you, if they run a trafficking network of people, they would most certainly use it to move operatives into the United States,' he added.
'If they could do what they did in Moscow, in the United States, they would do it in a heartbeat. They want to do it.'
'And it's something we have to be very vigilant about when we have a border in which 9 million people have come across in the last three years.'
Migrants who cross the border may often be forced to wait several years for officials to examine their applications and make a decision on their status.
Most are freed to roam US streets, including 2 million 'high-priority' cases of career criminals seeking asylum.
At the end of fiscal year 2023 on September 30, more than 6 million people were recorded on what officials term the 'non-detained docket.'
And Government projections, as communicated in Homeland Security documents sent to Congress, suggest the backlog will have risen to 8 million by October 1.
Isis-K regards the US, Russia, Iran and even their Taliban hosts in Afghanistan as enemies.
Its attack in Moscow was the deadliest on European soil for more than 20 years and one which they would love to replicate in the US according to Morgan Lerette, a former US Army captain and Blackwater contractor.
'It's only going to take a few of them to get armed and attack a large event, a concert, baseball game, Times Square to bring terrorism to US soil,' he added.
Basel Bassel Ebbadi, 22, admitted he was a member of Hezbollah and had come 'to make a bomb' when he was intercepted by agents at the Texas border with Mexico on March 9
And Colin Clarke, an analyst at Soufan Group security consulting firm, warned that they would not need enormous resources or many operatives to cause carnage once they got here.
'A terrorist is going to have a hard time building a bomb or purchasing a gun here, but low cost attacks are still possible, like a car or truck ramming,' he said. 'Anything is possible.
'It's common for terror groups to see an attack gain momentum, which may see sympathizers taking action elsewhere.
'There's no question this latest attack in Moscow will inspire others to act on behalf of ISIS.'