A Chinese mainland spokesman slammed the United States for a defense bill with provisions aimed at improving Taiwan's military capabilities.

US President Joe Biden signed into law the National Defense Authorization Act for fiscal year 2022 on Monday, which requires the US to continue supporting Taiwan to develop a sufficient self-defense capability.

The bill said cooperation between the US National Guard and Taiwan would be enhanced and Taiwan should be invited to the 2022 Rim of the Pacific Exercise, a large-scale international maritime military exercise hosted every two years near Hawaii.

Ma Xiaoguang, a spokesman for the Taiwan Affairs Office of the State Council, on Wednesday expressed firm opposition against the US for passing the bill, saying the Taiwan question is China's internal affair and the US has no right to interfere.

"No one and no force can stop our resolve and ability to thwart the provocations for 'Taiwan independence' and safeguard the country's sovereignty and territorial integrity," Ma said at a news conference.

The Democratic Progressive Party of Taiwan, who are willing to play as a pawn of the US and seek "independence" by relying on the US, is doomed to failure, he added.

Tensions have been manifested across the Straits this year. The People's Liberation Army has made about 950 flights near the island this year, higher than the 380 flights last year, island data showed.

When asked about the prediction for next year's military exercises in the Taiwan Straits, Ma said, the situation across the Straits next year will become more complex and grave.

"Our struggle against the DPP authorities' provocations for 'independence' and the interference of foreign forces may become more acute and intense," he said.

Ma said it's firmly believed that the mainland has the initiative in cross-Straits relations and will do the utmost to strive for the prospects of peaceful reunification of the country.

"If the 'Taiwan independence' secessionist forces make provocations and even cross the red line, we will have to take decisive measures," he said.