The U.S. military on Monday disclosed a jump of more than 50 percent in cases of traumatic brain injury stemming from Iran's missile attack on a base in Iraq last month, with the number of service members diagnosed climbing to over 100.

Iran launched ballistic missiles against two facilities in Iraq where U.S. troops were based on January 8, in retaliation to the U.S. killing of Revolutionary Guard General Qassem Soleimani in a drone strike at the Baghdad airport earlier.

Iran claimed that the strikes killed over 80 U.S. and allied troops. Meanwhile, the U.S initially insisted there had been no injuries, but has since revised that assessment repeatedly.

Trump says 'all is well' after Iran strikes U.S. bases in Iraq

The missile attacks capped a spiral of violence that had started in late December. Both sides have refrained from further military escalation, but the mounting number of U.S. casualties could increase scrutiny on the Trump administration's approach to Iran.

The Pentagon confirmed on Monday that so far 109 U.S. service members had been diagnosed with mild traumatic brain injury, of which 76 or 70 percent of them had returned to duty. There were no additional details on the status of the remaining 33.

Symptoms of concussive injuries include headaches, dizziness, sensitivity to light and nausea. 

Pentagon officials have repeatedly said there has been no effort to minimize or delay information on concussive injuries. But the disclosures following Tehran's attack have renewed questions over the U.S. military's policy regarding how it internally reports suspected brain injuries and whether they are treated publicly with the same urgency as loss of limb or life.

U.S. President Donald Trump appeared to play down the brain injuries last month, saying he "heard that they had headaches and a couple of other things" following the attack, prompting criticism from lawmakers and a U.S. veterans group.

Various health and medical groups for years have been trying to raise awareness about the seriousness of brain injuries, including concussions.

Since 2000, about 408,000 service members have been diagnosed with traumatic brain injury, according to Pentagon data.

(With input from Reuters)