By Michael Hernandez

WASHINGTON

The U.S. has obtained blood and urine samples from a suspected chemical attack in Syria that have tested positive for both an unidentified nerve agent and chlorine gas exposure, according to a report published Thursday.

Two anonymous officials were "confident", but not one hundred percent certain, in the intelligence, NBC News reported.

The U.S. officials told the American news outlet that the Assad regime is known to have used a mixture of chlorine and the nerve agent sarin in previous attacks. They also said the U.S. in conjunction with other countries has compiled intelligence, including images, that indicates the Assad regime carried out last weekend's fatal attack.

The White House and National Security Council did not immediately respond to Anadolu Agency's requests for comment on the report.

The White Helmets, a Syrian civil defense agency, blamed the Assad regime for the Saturday night chemical attack in the city of Douma in Eastern Ghouta, which it said killed 78 civilians and injured hundreds of others.

The U.S is currently assessing eight targets for a potential military response, sister news outlet CNBC separately reported. The sites reportedly include "two Syrian airfields, a research center and a chemical weapons facility".

U.S. Defense Secretary James Mattis said Thursday President Donald Trump has yet to decide on whether he will pursue military action in Syria.

"We have not yet made any decision to launch military attacks into Syria," Mattis told lawmakers on the House Armed Services committee. "The president has not made that decision."

Asked what worries him most about possible military action the U.S. might take, Mattis said: "On a strategic level, it's how do we keep this from escalating out of control."

Earlier Thursday, Trump appeared to walk back earlier comments in which he warned Russia to brace for missiles which he said "will be coming."

"Never said when an attack on Syria would take place. Could be very soon or not so soon at all!" Trump said Thursday on Twitter.

Later, he told reporters a decision will "be made fairly soon."