Chinese and Russian military chiefs targeted the United States for criticism at a security forum in Beijing on Monday, even as China’s second most senior military commander vowed to boost defense ties with Washington.

The lack of regular communications between the U.S. and Chinese militaries has been a worry for Washington as tensions rise over various issues and given the risks of an accidental clash in the South China Sea or near Taiwan.

The Xiangshan Forum, China’s biggest annual show of military diplomacy, began on Sunday without a Chinese defense minister, who typically hosts the event, but including a U.S. delegation.

Russian Defense Minister Sergei Shoigu warned the West that its involvement in the Ukraine war created grave danger.

“The Western line of steady escalation of the conflict with Russia carries the threat of a direct military clash between nuclear powers, which is fraught with catastrophic consequences,” Russia’s TASS state news agency cited Shoigu as saying at the forum.

Shoigu said the West intended to inflict “strategic defeat” on Russia in what he called a “hybrid war,” and praised Russia-China relations as “exemplary,” Russian state media reported.

Zhang Youxia, vice chairman, under President Xi Jinping, of China’s Central Military Commission, delivered veiled criticism of the United States and its allies, accusing “some countries” of trying to undermine China’s government.

But Zhang also stressed the need for improving military ties with the United States.

“We will deepen strategic cooperation and coordination with Russia and are willing to, on the basis of mutual respect, peaceful coexistence and win-win cooperation, develop military ties with the U.S.,” Zhang said in an address closely watched by military attaches and diplomats.

Zhang held talks with Shoigu on the sidelines of the forum, China’s Xinhua state media reported.

China’s defense minister has in previous years delivered the forum’s keynote speech but Li Shangfu was sacked as defense minister last week without explanation and a replacement has not been named.

Reuters reported last month that Li, who has been missing for two months, was being investigated over corruption.

China and the U.S. have had no high-level military-to-military communications since the Washington-sanctioned Li was appointed in March.

‘Here and listening’

The U.S. defense department has sent a delegation led by Cynthia Xanthi Carras, China country director in the Office of the Undersecretary of Defense.

Carras had a brief exchange with defense ministry spokesperson Wu Qian at the forum, a social media account affiliated with state broadcaster CCTV reported.

Chad Spragia, a former U.S. deputy assistant secretary of defense for China, stressed the importance of U.S. participation.

“It’s important for the U.S. to be here and not cede the space to others. We’re here and we’re listening,” said Sbragia, who said he was attending there in a research capacity.

The participation of the U.S. delegation comes as the United States and China ramp up exchanges ahead of an expected summit between U.S. President Joe Biden and China’s Xi next month.

Last week, China’s top diplomat, Wang Yi, met Biden for an hour in talks the White House described as a “good opportunity” to keep open lines of communication between the two rivals.

Despite the conciliatory remarks about improving China-U.S. military ties, Zhang and some Chinese military officers gave no sign of a softer stance on issues such as Taiwan, which Beijing’s regards as its territory.

Chinese Lieutenant-General He Lei, speaking at a panel on Sunday, said that if China were to have to use force against Taiwan, “it will be a war for reunification, a just and legitimate war.”

In his speech, Zhang said that countries “should not deliberately provoke other countries on major and sensitive issues,” he said, adding that Taiwan was “a core interest” for China.

Many Western countries have either shunned the forum or are only sending low-level delegations.