China on Thursday expressed strong opposition to the annual defense policy bill passed by the US Senate, which contains a section inviting Taiwan to join military drills.

"We are firmly opposed to any country's military contact with Taiwan. Our position is consistent and clear," said Chinese Defense Ministry spokesperson Yang Yujun at a monthly briefing.

The US Senate passed an annual defense policy bill last Thursday that authorizes some $600 billion in defense spending for the 2016 fiscal year, and initiates measures that could help cut costs, according to reports.

"We urge the US side to abide by the three China-US joint communiques, properly settle the Taiwan issue, and maintain the healthy growth of military ties and overall relations between both countries," Yang said.

The Senate bill, passed last week, says that Taiwan "should be encouraged to participate in exercises that include realistic air-to-air combat training", as well as advanced training for its ground forces, attack helicopters and surveillance aircraft.

The Taiwan issue is a core issue in China-US relations. Principles for correctly handling the issue have been defined in the three China-US joint communiques signed in 1972, 1978 and 1982.

The US has pledged to abide by the one-China policy and the principles set out in the three joint communiques.

Military relationship between China and US have improved in recent years.

Central Military Commission Vice-Chairman Fan Changlong has completed a visit to the US in mid-June.

Fan and US army Chief of Staff Raymond Odierno witnessed the signing of the China-US Army-to Army Dialogue Mechanism at the National Defense University in Washington on June 12.

This is the first cooperation document to be signed by the two armies in recent years.

Guan Youfei, director of the Foreign Affairs Office of the Ministry of National Defense, said that the two armies could hold joint exercises on land next year.

Both sides discussed mutual trust mechanisms for reporting major military operations and the code of conduct on military encounters in the air and at sea, both signed last year, and vowed to reach agreement on the air-to-air annex to the code of conduct before President Xi Jinping visits the US in September.

Major General Yao Yunzhu, a senior researcher at the People's Liberation Army's Academy of Military Science, said the annex on air-to-air encounters aims to prevent crises, while the dialogue mechanism between the armies mainly helps with cooperation.

Xinhua contributed to this story.