WASHINGTON, Dec 4 (Reuters) - U.S. government agencies

will hold a classified briefing for all senators on Wednesday on

China's alleged efforts known as Salt Typhoon to burrow deep

into American telecommunications companies and steal data about

U.S. calls, according to officials and a notice seen by Reuters.

The FBI, Director of National Intelligence Avril Haines,

Federal Communications Commission chair Jessica Rosenworcel, the

National Security Council and Cybersecurity and Infrastructure

Security Agency are to take part in the briefing, the officials

said. Separately, a U.S. Senate subcommittee is planning to hold

a hearing on the Salt Typhoon hacking on Dec. 11, officials

said.