China vowed Wednesday it would not accept "criticism or pressure" over its ties with Russia, after Washington warned that it will hold Beijing responsible if Moscow makes gains in Ukraine.

Deputy Secretary of State Kurt Campbell said Tuesday that Washington would "not sit by and say everything is fine" after Beijing renewed pledges of cooperation with Moscow during a visit by Russia's top diplomat.

In response, foreign ministry spokesperson Mao Ning insisted that "China and Russia have the right to engage in normal economic and trade cooperation".

"This kind of cooperation should not be interfered with or limited, and China also does not accept criticism or pressure," she added on Wednesday.

The two countries have in recent years ramped up contacts, and their strategic partnership has only grown closer since Moscow's invasion of neighbouring Ukraine.

Analysts say China holds the upper hand in the relationship with Russia, with its sway growing as Moscow's international isolation deepens as its war drags on.

On Tuesday, the two said they would strengthen strategic cooperation as Foreign Minister Sergei Lavrov held talks with President Xi Jinping and top diplomat Wang Yi.

Xi told Lavrov that China attached "great importance" to relations with Moscow and "stands ready, with Russia, to strengthen bilateral communication, (and) strengthen multilateral strategic coordination", according to Chinese state broadcaster CCTV.

Xi and President Vladimir Putin have agreed to maintain "close exchanges" to ensure the steady development of their ties, the readout said.

- Continued support -

While China says it is a neutral party in the Ukraine conflict, it has been criticised for refusing to condemn Moscow for its offensive and for indirect support for the war effort by continuing to trade with Russia.

US officials have recently stepped up warnings to Beijing against providing indirect aid to the Russian war effort.

In Brussels last week, US Secretary of State Antony Blinken told reporters that "China continues to provide materials to support Russia's defence industrial base".

And Treasury Secretary Janet Yellen, who wrapped up a visit to China on Monday, said she had warned officials of the consequences of supporting Russia's military procurement.

Campbell reiterated on Tuesday that "we have told China directly, if this continues, it will have an impact on the US-China relationship".

"We will see this not as just a Russian unique set of activities but a conjoined set of activities backed by China but also North Korea," he told the National Committee on US-China Relations, an educational group.

"This is antithetical to our interests," he warned.

Beijing responded on Wednesday that it has "always played a constructive role" in seeking a resolution to the war in Ukraine.

"If any country is truly concerned about peace in Ukraine, and hopes for an early end to the crisis, they should first reflect on the root causes of the crisis," Mao said.