The Saudi embassy in Washington, D.C. today denied its government warned the U.S. about accused Boston bomber Tamerlan Tsarnaev.

According to a highly placed source who spoke to MailOnline, the Saudis sent a written warning about Tsarnaev to the U.S. Department of Homeland Security in 2012. That was long before pressure-cooker blasts killed three and injured hundreds.

The official told MailOnline about a written warning from the Saudi government to the Department of Homeland Security, and said he had direct knowledge of that document.

But the Middle Eastern nation's embassy in Washington denied that account on Wednesday.

It issued a statement which read: 'The Saudi government had no prior information about the Boston bombers. Therefore, it is not true that any information, written or otherwise, was passed to the U.S. Department of Homeland Security (DHS) or any other US agency in this regard,' an embassy statement statement claimed.

'The Saudi government also does not have any record of any application by Tamerlan Tsarnaev for any visa to Saudi Arabia.'

The Saudis' warning, the official told MailOnline, was separate from the multiple red flags raised by Russian intelligence in 2011, and was based on human intelligence developed independently in Yemen.

Citing security concerns, the Saudi government also allegedly denied an entry visa to the elder Tsarnaev brother in December 2011, when he hoped to make a pilgrimage to Mecca, the source said. Tsarnaev's plans to visit Saudi Arabia have not been previously disclosed.

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Was it preventable? A senior Saudi official says his country warned the U.S. about Tamerlane Tsarnaev in 2012, advising the federal government that he planned an attack on a major U.S. city

Did she know? Janet Napolitano (R) sits atop the Department of Homeland Security, the agency that allegedly received a detailed letter from the Saudi kingdom about Tsarnaev (L) and three Pakistani jihadis

The Saudis' warning to the U.S. government was also shared with the British government. 'It was very specific’ and warned that 'something was going to happen in a major U.S. city,' the Saudi official said during an extensive interview.

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.

As many as 4 million Muslims make pilgrimages annually to the Grand mosque in the city of Mecca. Tsarnaev sought to join them for an 'Umrah' journey, a trip that happens outside of the month reserved for the annual Hajj

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.'

'Just like the different agencies in the Boston JTTF [Joint Terrorism Task Force] want credit for breaking the Tsarnaev case,' the aide added, 'they sometimes jealously guard the very intel they should be sharing the most freely. Sometimes it makes no sense at all.'

Obama said Tuesday that an inter-agency review would leave no stone unturned in an effort to learn whether government agencies could have done more to prevent the Boston bombings

House Homeland Security Committee chairman Mike McCaul plans to announce on Wednesday an investigative hearing to probe what U.S. intelligence knew prior to the Boston attacks, two senior Republican sources told MailOnline.

Separately, President Obama announced Tuesday that the U.S. government will launch a wide-ranging inquiry into the sharing of information among the Federal Bureau of Investigation, the Department of Homeland Security and other intelligence and law-enforcement agencies of the federal government.

'We want to leave no stone unturned,' the president said in a rare White House press conference.

The internal review will be led by Director of National Intelligence James Clapper and several inspectors general.

'This is not an investigation,' Clapper’s spokesman Shawn Turner said in a prepared statement. 'This is an independent review of information-sharing procedures. It is limited to the handling of information related to the suspects prior to the attack.'

It is not yet clear whether information from Saudi Arabia will be involved in Clapper's inter-agency review.

Eight-year-old Martin Richard was among the three people killed in the explosions at the finish line of the Boston Marathon on April 15

Chaos: The bombing left thousands running for their lives and sent more than 200 to hospitals, including some whose limbs were torn off their bodies by the force of the blasts

Utah Republican Rep. Jason Chaffetz appeared on CNN Tuesday afternoon, upbraiding the Obama administration for presuming that the federal government's handling of intelligence prior to the Boston bombings was appropriate and effective.

'As soon as the bombing happened we had officials, locally and from the feds, saying, "Oh, this was an isolated case, there was just one person involved." We didn't know that,' Chaffetz said.

The 'starting point' for a federal investigation, he said, must be, 'This is unacceptable, we will not stand for it, we will get to the bottom of it, and we will not rest until we figure it out.'

'Mr. President,' he said, addressing Obama, 'the starting point should be an intolerance that this thing happened.'

GOP momentum? House Homeland Security Committee chair Mike McCaul (L) plans to convene a hearing to investigate the government's failure to prevent the Boston bombings. Utah Rep. Jason Chaffetz (R), who serves on that committee, said on CNN that an inquiry should not presume all is well

The high-ranking Saudi official whom MailOnlne interviewed at length provided a wealth of detail about the warning he says his government sent to the United States. He spoke on condition of anonymity because he is not authorized to talk publicly about foreign intelligence, or about Saudi Arabia’s diplomatic relationship with the United States.

He suggested that the Saudi Ministry of Interior sent the letter out of an abundance of caution in order to be helpful to the United States, even though its intelligence on Tsarnaev wasn't yet fully developed.

'With Saudi Arabia it's always code red,' he said. 'There's no code orange, or code yellow. Always red.'

The Saudi government, he added, alerted the U.S. in part because it believed American authorities should be inspecting packages that came to Tsarnaev in the mail in order to search for bomb-making components.

Saudi Interior Minister Prince Mohammed bin Nayef bin Abdulaziz (L) met with President Obama in January. His counterpart in the Saudi foreign ministry, Prince Saud bin al-Faisal (R), had an unscheduled meeting with Obama in the Oval Office just two days after the Boston bombings

The written warning also allegedly named three Pakistanis who may be of interest to British authorities. The official declined to provide more details about the warning to the UK, but said the two governments received the same information.

The Ministry of Interior, he said, sent the letters in 2012, likely after Tsarnaev returned from Russia to the United States in July.

President Barack Obama's published schedule indicates that he met in the Oval Office with Prince Mohammed bin Naif bin Abdulaziz, the Saudi Interior minister, on January 14, 2013.

The Saudis denied Tsarnaev entry to the kingdom when he sought to travel to Mecca in December 2011 for a pilgrimage known as an Umrah – one that is undertaken during months that don’t fall within the regular Hajj period of the year.

That rejected application came one month before he traveled to Russia, where U.S. intelligence sources believe he acquired training enabling him to construct and detonate the bombs that he and his younger brother placed hear the Boston Marathon’s finish line.

The younger brother, Dzhokhar Tsarnaev, is in federal custody at a prison medical facility.

Celebration turned to mourning on April 15 after Tamerlan Tsarnaev and his younger brother Dzhokhar allegedly detonated two powerful bombs near the finish line of the Boston Marathon, killing 3 and injuring more than 200

The Saudi official who spoke to MailOnline speculated that Tsarnaev's residence in the United States might have made it more difficult for him to gain entry into the kingdom.

'U.S.-based Muslims who become radicalized and want to visit Mecca create an unusual problem,' he said, compelling the Saudi government 'to carefully examine applications.'

In the wake of the April 15 Boston Marathon bombings, Saudi Foreign Minister Prince Saud al-Faisal met with Secretary of State John Kerry on April 16, and then had an unscheduled meeting with President Obama on April 17.

'This is the DNA of the Saudi government,' said the Saudi official, referring to officials in the royal court in Riyadh. 'This is how they work. They sent the letter, but that wasn't enough. They then sent the top guy to meet personally with the president.'

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.'

Richard Reid (L) was apprehended after a failed attempt to blow up an airliner with bombs concealed in his shoes. The Saudi government provided specific intelligence about Reid to the U.S., and now it has been revealed that they wrote to the American government about Tamerlan Tsarnaev (R) in 2012

Tamerlan may have boasted about his plans online, the Saudi official said, offering an explanation for how Yemen-based sources first learned of him. Islamist militants have well-developed social networks that can enable news to migrate quickly across vast distances.

The Saudi government sometimes tracks such radicals by launching fake jihadi websites to attract extremists. The Ministry of Interior then tracks them electronically, often across the world, and shares information with governments it considers friendly, including the United States.

'The Saudi Arabian government is doing everything it can to wipe out these people and treat America as a true friend,' the official said.

The Saudi intelligence services have a long history of providing credible information to America and Great Britain about looming threats.

'This is the fourth time the Saudi Arabian government has given the U.S. specific intel' about a possible terror plot, the official said, citing prior warnings about Richard Reid, the so-called shoe bomber who repeatedly tried to light a fuse in his shoe to bring down American Airlines flight 63 bound for Miami in December 2001.

He also cited the 300-gram 'ink-cartridge bombs' planted on two cargo planes headed for the United States from Yemen in October 2010. Those explosives were intercepted in Dubai, and at an East Midlands airport in Great Britain.

The terror: A Boston firefighter carried an injured girl away from the scene after the Boston Marathon bombings. In all, Tsarnaev is believed to have killed three Americans, including an eight-year-old boy

Tamerlan Tsarnaev's namesake was a 15-century Central Asian warlord who referred to himself as ‘the sword of Islam.’ Sometimes spelled 'Tamerlane' in English, he was known for his cruelty.

When he conquered Baghdad, he reportedly made a pyramid of human skulls from unfortunate residents of that city.

Although still revered in Chechnya and throughout Central Asia, the original Tamerlane is sometimes vilified in modern-day Saudi textbooks.