President Joe Biden vowed Tuesday he would not hesitate to defend US interests against China after he ordered the downing of a suspected surveillance balloon but, delivering his State of the Union address, kept the door open to cooperation.

In the annual speech to assembled lawmakers, many of whom have pressed for a hard line on China, Biden called for US investment in the military, technology and alliances to take on the country widely viewed as the chief US competitor.

"I'm committed to work with China where it can advance American interests and benefit the world," Biden said.

"But make no mistake about it -- as we made clear last week, if China threatens our sovereignty, we will act to protect our country. And we did," he said to applause.

Biden said that "winning the competition" with China should unite Americans.

"I will make no apologies that we are investing to make America stronger -- investing in American innovation, in industries that will define the future that China intends to be dominating."

But Biden steered clear of hawkish language as he mentioned by name his Chinese counterpart, Xi Jinping, whom he met at length in November in Indonesia.

Biden said he told Xi that "we seek competition, not conflict."

In a foreign ministry statement issued after Biden's address, China vowed to "firmly defend" its interests, but also said it was "opposed to using competition to define the entire Sino-US relationship."

It went on to urge the United States to "pursue a positive and pragmatic China policy, and work with China to push Sino-US relations back to the track of healthy and stable development."

China was one of the few foreign policy issues mentioned by Biden in a more than one-hour speech that comes as he prepares for a likely run for a second term.

He also promised long-term support for Ukraine but made no mention of Iran, the Israeli-Palestinian conflict, North Korea or this week's devastating earthquake in Turkey and Syria.

Pentagon says China rejected talks

A US fighter jet on Saturday shot down what the Pentagon called a Chinese surveillance balloon after it floated out over the Atlantic Ocean, with the military saying it had waited until a point when the debris could not hurt people on the ground.

The episode led US Secretary of State Antony Blinken to postpone a visit to Beijing aimed at reducing tensions as he accused China of violating US sovereignty.

Blinken said he sought to maintain communication with China. But at the Pentagon, a spokesman said that China rebuffed a request to speak.

Defense Secretary Lloyd Austin requested a secure call with his Chinese counterpart Wei Fenghe immediately after the shootdown, Brigadier General Pat Ryder said.

"Unfortunately, the PRC has declined our request. Our commitment to open lines of communication will continue," Ryder said, referring to the People's Republic of China.

China says the balloon was an errant weather observation aircraft with no military purpose. But Washington has described it as a sophisticated high-altitude spying vehicle which reportedly traversed over several top-secret military sites.

Austin and Wei met in Cambodia in November as Washington and Beijing sought to lower the temperature after a visit to Taiwan by then-speaker of the House Nancy Pelosi that enraged China.

General Glen VanHerck, head of the US Northern Command, said a naval ship would map a debris field left by the balloon in the Atlantic that is expected to measure about 1,500 by 1,500 meters (yards).

The balloon itself was up to 200 feet (60 meters) tall and carried a payload weighing several thousand pounds that was roughly the size of a regional jet aircraft, he said.

VanHerck said the balloon debris would be carefully studied.

"I don't know where the debris is going to go for a final analysis, but I will tell you that certainly the intel community along with the law enforcement community that works this under counterintelligence will take a good look at it," he said.

© Agence France-Presse