China on Tuesday rejected charges by two key U.S. senators that Beijing was failing to control a flood of counterfeit parts installed on U.S. weapons systems.

Senate Armed Services Committee Chairman Carl Levin said committee investigators had identified about 1,800 cases involving one million counterfeit parts since 2009, and those numbers were just the tip of the iceberg.

Parts for defence systems are bought from many sources, which often are infiltrated with counterfeit items, the senators said. China has been identified nearly five times more frequently than any other country as a source of counterfeit parts, according to a U.S. Commerce Department report.

Chinese Foreign Ministry spokesman Hong Lei, asked about those comments, said China was committed to fighting fake products.

The Chinese government has always paid a great deal of attention to, and has promoted, cooperation with relevant overseas bodies in the fight against counterfeits. This is universally acknowledged, Hong told a daily news briefing.

He did not elaborate.

Levin said that rather than cooperating, Chinese authorities had impeded the committee's investigation, with one embassy official telling them it could be damaging to U.S.-China relations.

Senator John McCain, the top Republican on the committee, said the issue needed to be addressed urgently because counterfeit parts posed real dangers to U.S. troops and contributed to the high costs of weapons systems.

Last week, a U.S. intelligence report concluded that China was the most active and persistent country using cyber espionage to steal U.S. trade and technology secrets.

McCain and Levin said various measures were being considered to address the issue, including amendments that would clearly spell out that contractors should be held responsible for the cost of replacing any counterfeit parts.

(Reporting by Ben Blanchard)