CIA Director Mike Pompeo has said that a “couple hundred Russians” were killed in eastern Syria during an encounter with U.S. Special Operations Forces. The U.S. artillery and air strikes in early February get the job done in an attack that remains shrouded in mystery.

The comments by Pompeo, which came during his testimony before a Senate committee on April 12, was a rare open acknowledgment by a top U.S. official about the incident.

Speaking during a hearing to consider his nomination to be the next U.S. secretary of state, Pompeo also said he would seek a tougher approach toward Russia.

He said President Donald Trump’s administration had been tough in its policies toward Moscow, citing the recent Treasury sanctions imposed on Russian business and political figures, and the expulsion of dozens of Russian diplomats.

But he said Russian President Vladimir Putin “has not yet received the message sufficiently and we need to continue to work at that.”

“But it hasn’t just been sanctions, the largest expulsion of 60 folks was from this administration,” he added.

“In Syria, now, a handful of weeks ago the Russians met their match. A couple hundred Russians were killed. The list of actions that this administration has taken…. I’m happy to walk through each of them but I don’t want to take up more time,” he said.

U.S. military commanders had previously said that a massive ground and air assault was launched on February 7 against a column of fighters and weaponry in the eastern Syrian province of Deir al-Zor. The assault was launched immediately after a base housing U.S.-backed fighters from the Syrian Democratic Forces and U.S. military advisers was attacked.

U.S. officials earlier said more than 100 pro-government Syrian fighters had been killed, and that AC-130 gunships, F-15 and F-22 fighter jets, and Apache helicopter gunships had been used in the U.S. assault, along with Marine Corps artillery units.

No U.S. personnel were injured in the attack. In Moscow, Russian officials said no uniformed Russian troops were involved in the attack. Some Russia related news media claimed that most of the killed Russians were working as private military contractors.