Tsarnaev Brothers
Dzhokhar (l.) Tsarnaev says the U.S. wars in Iraq and Afghanistan motivated him and his brother to carry out the Boston bombings. FBI

The U.S. wars in Iraq and Afghanistan motivated the two suspects in the Boston Marathon bombings to commit the terror attacks, Dzhokhar Tsarnaev reportedly told his interrogators.

Tsarnaev, 19, who is being questioned about his role in the attacks from his hospital bed at Boston's Beth Israel Deaconess Medical Center, confessed to planting one of the bombs near the finish line on April 15, the Washington Post reported, citing “U.S. officials familiar with” the questioning.

When questioned about the motive for the bombings, Tsarnaev “specifically cited the U.S. war in Iraq … and the war in Afghanistan,” according to the Post.

The Iraq war ended in December 2011, when the last American troops withdrew from the country. President Barack Obama said he expects to end combat operations in Afghanistan in 2014.

An elite team of investigators from various federal agencies is questioning Tsarnaev about the bombings, and preliminary information suggests the 19-year-old college student and his brother, 26-year-old Tamerlan Tsarnaev, became “self-radicalized” and did not have help from outside terrorist groups in carrying out the attacks.

The elder Tsarnaev died in an early Friday morning after exchanging gunfire with authorities, which followed a carjacking and the fatal shooting of MIT police officer Sean Collier.

The bombings, which detonated near the finish line of the Boston Marathon near Copley Square in Boston, killed three people and injured more than 170 others.

The Tsarnaevs learned to make their bombs, which were composed of ball bearings, metal shards and BBs, from the online magazine “Inspire,” which is published by Al-Qaeda, NBC News reported. The bombs were housed inside pressure cookers in accordance with the article's instructions.

As they investigate the case, authorities are particularly interested in a trip to Russia that the elder Tsarnaev took last year. Investigators have yet to find evidence that Tamerlan Tsarnaev received guidance on carrying out the attacks during the trip, the Post reported.

While the younger Tsarnaev told investigators that he and his brother acted alone, investigators are trying to confirm his statements.

A U.S. intelligence official told the Post that other evidence backs up the 19-year-old suspect’s claims.

“These are persons operating inside the United States without a nexus” to a terrorist group, the source told the Post.

Meanwhile, Russia has accused the United States of not taking Tamerlan Tsarnaev's case as seriously as it should. The U.S. countered by saying that Russia didn’t appear very concerned about his overseas trip, the U.S. official told the Post.

“The evidence points to the fact that they let him into the country [Russia] and let him out of the country,” the official said. “They didn’t take any legal action, which they could have while he was there.”