WASHINGTON (Reuters) - Hackers associated with the Chinese government have repeatedly breached the computer systems of U.S. companies, including airlines and technology firms, that are involved in the movement of U.S. troops and military equipment, a U.S. Senate panel has found.

The Senate Armed Services Committee's year-long probe, details of which were made public on Wednesday, found that U.S. Transportation Command, or Transcom, was only aware of two out of at least 20 such cyber intrusions within a single year.

The committee's investigation also found gaps in reporting requirements and a lack of information sharing among government entities. That in turn left the U.S. military largely unaware of computer compromises of its contractors.

"These peacetime intrusions into the networks of key defence contractors are more evidence of China's aggressive actions in cyberspace," Senator Carl Levin, the committee's chairman, said in releasing the report.

The committee found that in a 12-month period beginning June 1, 2012, there were about 50 intrusions or other cyber events into the computer networks of Transcom contractors.

At least 20 of those were successful intrusions attributed to an "advanced persistent threat," a term used to designate sophisticated threats commonly associated with governments.

All of those intrusions were attributed to China.