During his secretary of state confirmation hearing Thursday, CIA Director Mike Pompeo said that “a couple hundred Russians” were killed by the U.S. in Syria a few weeks ago, an unexpected boast about an incident that both sides have been reluctant to discuss.

Pompeo’s remark came in response to a question from Sen. Jeanne Shaheen about whether the Trump administration was doing enough to hold Vladimir Putin’s government accountable. Pompeo answered:

It hasn’t just been sanctions, the largest expulsion of 60 folks was from this administration. This administration announced a nuclear posture review that has put Russia on notice that we are going to recapitalize our deterrent force. In Syria, now, a handful of weeks ago the Russians met their match. A couple hundred Russians were killed.

Pompeo seems to be referring to a Feb. 7 incident in which the U.S. launched an airstrike against pro-Assad forces near Deir al-Zour, Syria, after U.S.-backed Kurdish troops believed they were under attack. This is one of several incidents in which the U.S. has attacked pro-regime forces in “self-defense” over the past year. Reports quickly began to trickle out that a number of Russians embedded with the Syrians, ranging from “dozens” to 300, were killed in the attack.

Russia initially admitted that five Russians had been killed but in a later statement said that “several dozen” had died in a recent armed clash. The Russian statements have stressed that these were “volunteers” rather than Russian army personnel. They were most likely affiliated with the Wagner Group, a Russian military contractor. (One of Wagner’s key investors Yevgeny Prigozhin, nicknamed “Putin’s chef,” is currently under U.S. sanction, partly due to his role in the “troll farm” International Research Agency.) As with the conflict in Ukraine, the Russian government prefers not to discuss the role played by Russian mercenaries in Syria, though the recent incident has provoked an unusual public outcry from the families of those killed.

The U.S. has not pressed Russia on the role of its citizens in the incident and has been mostly reluctant to discuss it. A U.S. military spokesman told the New York Times that the U.S. was in contact with Russian forces during the attack and that “Russian officials assured coalition officials they would not engage coalition forces in the vicinity.” Secretary of Defense James Mattis said on Feb. 11 that “the Russians profess that they were not aware when we called about that force that had crossed [the deconfliction line],” adding that “we go out of our way to ensure that we do not endanger the Russians.”

Brig. Gen. Jonathan Braga, director of operations for the U.S.-led anti-ISIS coalition, recently discussed the incident with NBC News. When asked about reports that 200 or 300 Russians had been killed, he said, “We’ve seen that in open reports as well and that’s I would say close to our estimates as well.”

It’s understandable that Pompeo would want to highlight the range of actions the administration has taken against the Russian government, Trump’s own comments notwithstanding. But given that the risk of the U.S. striking Russian personnel and further escalation of conflict between the United States and Russia is a major concerns as the U.S. contemplates new airstrikes against the Assad regime, this was an odd moment to bring up an incident that both governments seem anxious to sweep under the rug.