More than 100 US troops sustained “mild” traumatic brain injury, far more than originally announced, after Iran launched missiles at their base in Iraq last month, according to the Department of Defense.

“As of today, 109 US service members have been diagnosed with mild traumatic brain injury, or mTBI, an increase of 45 since the previous report,” the Pentagon said in a statement on Monday.

Of them, 76 have returned to duty while most of the rest are still undergoing evaluation and treatment.

The statement further said that 27 troops have been transported to Germany for further evaluation, while 21 returned to the US.

“This is a snapshot in time and numbers can change,” the statement added.

According to the Pentagon and President Donald Trump, initially, there were no service members who were wounded or killed in the Iranian missile attack, which was retaliation for the January 2 US drone strike that killed a top Iranian general.

Iran fired ballistic missiles at the base to retaliate for the January 3 US drone strike that killed top Iranian general Qasem Soleimani while he was in Baghdad.

Trump was understood to downplay the impact on US troops to help ratchet down tensions between the two countries, amid concerns that a full war could break out.

Earlier on Monday, Pentagon press secretary Alyssa Farah said in a statement, “We are grateful to the efforts of our medical professionals who have worked diligently to ensure the appropriate level of care for our service members, which has enabled nearly 70 per cent of those diagnosed to return to duty”.

Last month, President Trump said he does not consider potential brain injuries to be as serious as physical combat wounds, downplaying the severity of the injuries suffered in Iraq.

During the World Economic Forum in Davos, Switzerland, Trump was asked to explain the discrepancy between his previous comments that no US service member was harmed and reports of US troops being treated for injuries suffered in the attack.

The Centers for Disease Control and Prevention defines a TBI as a “disruption in the normal function of the brain” that’s typically caused by a bump, a blow or a jolt to the head. One of the most common forms of TBI is a concussion, also known as mild TBI (mTBI).

According to the CDC, in 2014, very severe cases can even result in death. There were 56,800 TBI-related deaths in the US.

(With inputs from agency)