Six US troops in Syria suffered traumatic brain injuries during two attacks last week by Iran-backed militants, the Pentagon said on Thursday.

The US military said they were diagnosed during routine screenings in recent days.

The disclosure further raises the human toll among American forces from strikes and counterstrikes in Syria last week to a total of 12 US troops wounded. The attacks also killed an American contractor and injured another.

This will add more political pressure on the Biden Administration to deter Iran from supporting such attacks in the region.

In Congressional hearings last week and this week, Republican lawmakers accused the administration of being soft on Tehran, which they said is not deterred from killing and injuring Americans.

Of 83 attacks in Iraq and Syria since President Joe Biden took office, just four retaliations have taken place, according to the Pentagon.

Senator Tom Cotton, addressing Secretary of Defense Lloyd Austin in a hearing on Wednesday, said, “What kind of signal do we think this sends to Iran when they can attack us 83 times since Joe Biden has become president and we only respond four?”

Republicans also accuse the administration of not informing Congress in a timely manner on March 23, while the Senate was debating a bill related to the issue of US forces stationed in the Middle East.

While Austin insisted Wednesday the information was relayed as soon as possible, his attempts to appease the Republicans fell on deaf ears.

“I don't believe you,” slammed Senator Cotton. “I believe that your office specifically withheld notification of this deadly strike against Americans because of the Rubio amendment on which we voted at midday directly touched on exactly this scenario, not repealing the use of force resolutions,” suggesting that the information was withheld because “the President couldn't certify that Iran was no longer attacking us in Iran and Syria”.

Pentagon spokesman Brigadier General Patrick Ryder said four service members suffered traumatic brain injuries at the US base near the Syrian city of Hasaka during a drone attack on March 23. Two others suffered injuries at mission support site Green Village during an attack on March 24.

"All personnel in the vicinity of a blast are screened for traumatic brain injury. So, these additional injuries were identified during post-attack medical screenings," Ryder told a news briefing.

The Pentagon also estimated eight militants were killed during retaliatory US air strikes against two Iran-linked facilities in Syria.

Ryder said the militants killed were not believed to be Iranian but were associated with the Islamic Revolutionary Guard Corps (IRGC).

That toll is lower than the one reported by a Syrian war monitoring group, which estimated that the air strikes and exchanges of fire killed three Syrian troops, 11 Syrian fighters in pro-government militias and five non-Syrian fighters who were aligned with the government.

President Joe Biden on Friday warned Iran that the United States would act forcefully to protect Americans.

The White House said on Monday that the incidents would not trigger a US pullback from its nearly eight-year-old deployment to Syria, where it is battling the remnants of Islamic State.

This is not the first time US troops in the region have been diagnosed with brain injuries from attacks.

In 2020, more than 100 US troops were diagnosed with traumatic brain injuries stemming from a missile attack by Iran against a base in Iraq.

Syria's foreign ministry has condemned last week's US strikes, saying Washington had lied about what was targeted and pledging on Sunday to "end the American occupation" of its territory.

Iran's foreign ministry accused US forces of “terrorist attacks” and targeting "civilian sites."

With reporting by Reuters