Secluded in his hideaway in Pakistan, Usama bin Laden suspected Iranian officials might implant tracking devices in his sons, according to a document released Thursday in a batch of materials seized in a 2011 raid that killed the Al Qaeda leader.

"If they inject you with a shot, this shot might be loaded with a tiny chip," bin Laden wrote in an undated letter to his sons, Uthman and Mohammed, who were being allowed to leave Iran. "The syringe size may be normal, but the needle is expected to be larger than normal size. The chip size may be as long as a seed of grain but very thin and smooth."

In its final hours, the Obama administration released the last of three installments of documents belonging bin Laden that were collected during the raid on his compound in Abbottabad, Pakistan.

In the second batch of documents, released last March, bin Laden also expressed the same paranoia in a letter to one of his wives, who also lived in Iran.

"I was told that you went to a dentist in Iran and you were concerned about a filling she put in for you," bin Laden wrote. He said he wanted to be told of any concerns she or any of his followers had about "chips planted in any way."

Tracking down and killing the man behind the 2001 terrorist attacks on America is one of President Barack Obama's greatest accomplishments.

Intelligence officials have worked for more than two years to declassify the hundreds of documents captured in the raid. The last batch, consisting of 49 documents, includes a running disagreement between bin Laden and Al Qaeda's affiliate in Iraq, which morphed into the Islamic State group. Those militants are currently the top target of U.S. counterterrorism efforts.

The Pentagon announced Thursday that the U.S. Air Force attacked a pair of IS military camps in Libya, seeking to eliminate extremists who had escaped from their former stronghold of Sirte.

Bin Laden is responsible for orchestrating the Sept. 11 strikes against the United States that killed nearly 3,000 people. The attacks drastically changed America's footprint abroad and challenged some of the most basic tenets of the Constitution in an effort to detect terrorists before they strike.

In a letter to a fellow militant, written after 9/11, bin Laden called on his followers to invent new ways to battle the West.

"If we cannot manufacture weapons like the weapons of the Crusader West, we can destroy its complicated industrial and economic system and exhaust its forces that fight without faith until they escape," he wrote.

"Therefore, the mujahidin had to create new methods that no one from the West can think about, and one of the examples of this creative thinking is using the airplane as a powerful weapon, like what had happened in the blessed attacks in Washington, New York and Pennsylvania."