The government of Saudi Arabia sent a letter to the US Department of Homeland Security in 2012 warning that "something was going to happen in a major US city" and specifically mentioned Tamerlan Tsarnaev, along with three Pakistanis, who might be a threat.

The story appears in the UK Daily Mail. The Saudis denied Tamerlan a visa to visit Mecca in 2011, believing he had been radicalized. The warning came following his trip to Russia in 2012 and came from sources in Yemen.

It "did name Tamerlan specifically," he added. The 'government-to-government' letter, which he said was sent to the Department of Homeland Security at the highest level, did not name Boston or suggest a date for his planned attack.

If true, the account will produce added pressure on the Homeland Security department and the White House to explain their collective inaction after similar warnings were offered about Tsarnaev by the Russian government.

A DHS official denied, however, that the agency received any such warning from Saudi intelligence about Tamerlan Tsarnaev.

'DHS has no knowledge of any communication from the Saudi government regarding information on the suspects in the Boston Marathon Bombing prior to the attack,' MailOnline learned from one Homeland Security official who declined to be named in this report.

The White House took a similar view. 'We and other relevant U.S. government agencies have no record of such a letter being received,' said Caitlin Hayden, a spokesperson for the president's National Security Council.

The letter likely came to DHS via the Saudi Ministry of Interior, the agency tasked with protecting the Saudi kingdom's homeland.

A Homeland Security official confirmed Tuesday evening on the condition of anonymity that the 2012 letter exists, saying he had heard of the Saudi communication before MailOnline inquired about it.

An aide to a Republican member of the House Homeland Security Committee speculated Tuesday about why the Obama administration contradicted the knowledgeable Saudi official. 'It is possible the Department of Homeland Security received the information from the Saudi government but never passed it on to the White House,' the GOP staffer said. 'Communication between DHS and the White House's national security apparatus isn't always what it should be.'

'I can easily see it happening where one hand didn't know what the other was doing because of a turf war.'

Apparently, the hardened jihadists didn't think much of Tamerlan:

He dismissed the idea that Tamerlan Tsarnaev was likely trained by al Qaeda while he was outside the United States last year.

The Saudis' Yemen-based sources, he explained, said militants referred to Tamerlan dismissively as 'the volunteer.'

'He was a gung-ho, self motivated jihadi who wasn't tasked by a larger group,' he said.

'There is no reason for anyone in Afghanistan to have in his thinking a scenario like this,' the official added, referring to pressure-cooker bombs at the Boston Marathon. 'He took the initiative. That's why they call him "the volunteer."'

'The Boston thing is beneath them,' he said of al Qaeda. 'They don't think like this. This is like a firecracker to them. They want something big.'

What to make of this? It's important to keep things in perspective and realize that Tamerlan Tsarnaev was a small fish in a big ocean. But failing to pass along such a specific warning about a radicalized American Muslim is nearly unbelievable - if it indeed was specific - and smacks of a pre-9/11 mindset about aharing intelligence.

Picking up the threads of Tamerlan Tsarnaev's travels and finding out who was tracking him and why will be something that Congress is going to want to look into.