The top Democrat on the Senate intelligence committee said he wants the Trump administration to brief his members on how sensitive F-35 stealth warplane parts ended up in China’s possession.

“I’m trying to get a full brief on what happened, it’s extraordinarily concerning,” Senator Mark Warner of Virginia said in an interview, adding that he expects a briefing “by week’s end.”

The Pentagon is working to retrieve a cockpit canopy and weapons-bay door belonging to an Australian military F-35 fighter jet that were inexplicably diverted to Hong Kong while being sent to the US for inspection on a United Parcel Service Inc plane. Both parts — supplied by US defense giant Lockheed Martin Corp — were coated with radar-absorbing material that enhances their stealth capabilities.

At least two congressional committees are now investigating how the parts fell into the hands of the Chinese government. The intelligence committee briefing would add to the widening probe. The Chinese government later took possession of the parts but so far hasn’t returned them.