The United States on Saturday urged Russia to pull back from the brink over Ukraine, warning that the G7 and its allies will impose tough measures if it abandons diplomacy.

A senior State Department official told reporters at a meeting of the grouping's top diplomats in Liverpool, northwest England, that Moscow still had time to change course.

"But if they choose not to pursue that path, there will be massive consequences and severe costs in response, and the G7 is absolutely united in that," the official said.

"A large number of democratic countries will join us in imposing costs," they added.

The G7 foreign ministers meeting in Liverpool, northwest England, is the last in-person gathering of Britain's year-long presidency The G7 foreign ministers meeting in Liverpool, northwest England, is the last in-person gathering of Britain's year-long presidency Photo: AFP / Paul ELLIS

The warning came as Russian sabre-rattling against Ukraine and how to counter an increasingly assertive China dominated the first day of a two-day meeting of G7 foreign ministers in the British city.

The meeting -- at which ministers want to present a united front against authoritarianism -- is the last in-person gathering of Britain's year-long G7 presidency, before it hands the baton to Germany.

Opening the talks, Britain's Foreign Secretary Liz Truss told delegates: "We need to come together strongly to stand up to aggressors who are seeking to limit the bounds of freedom and democracy.

"To do this, we need to have a fully united voice. We need to expand our economic and security posture around the world."

Truss, in the job since September, set out her foreign policy vision in a major address on Wednesday, echoing US threats of unprecedented sanctions if Russia invades Ukraine.

US Secretary of State Antony Blinken is attending the meeting before flying on to Indonesia, Malaysia and Thailand next week US Secretary of State Antony Blinken is attending the meeting before flying on to Indonesia, Malaysia and Thailand next week Photo: POOL via AFP / OLIVIER DOULIERY

Western concerns are growing over a Russian troop build-up on the border that the Kremlin says is defensive against any move by the former Soviet state eastwards towards NATO.

G7 ministers want to show the grouping can move beyond condemnation to robustly defend its values as a deterrent to future threats.

The meeting comes after US President Joe Biden this week held a virtual summit with his Russian counterpart Vladimir Putin to try to end the stand-off diplomatically.

Washington's top diplomat for Europe and Eurasian affairs, Karen Donfried, jets to Kiev and Moscow next week for follow-up talks with senior government officials.

She will then head to Brussels for further discussions with NATO and EU allies.

UK Foreign Secretary Liz Truss called for Western unity against threats from countries such as China and Russia UK Foreign Secretary Liz Truss called for Western unity against threats from countries such as China and Russia Photo: POOL via AFP / Paul ELLIS

US Secretary of State Antony Blinken flies on to southeast Asia next week on a visit designed to highlight the region's importance in Washington's push for "peace, security and prosperity" in the Indo-Pacific region against China.

Britain's G7 presidency has been dominated by responding to Beijing's alleged widespread domestic rights abuses, as well as creeping authoritarianism in its former colony, Hong Kong.

This week, a panel of human rights lawyers and experts in London concluded China had committed genocide by imposing population restrictions, including birth control and forced sterilisations, on its Muslim minority Uyghurs.

China rejected the tribunal's findings.

Biden has pushed the G7 for a stronger collective stance towards both Russia and China, and this week saw Washington, London and Canberra announce diplomatic boycotts of the 2022 Beijing Winter Olympics.

In Liverpool, delegates want to end the "strategic dependence" of a growing number of low- and middle-income countries on the G7's adversaries, in various areas from energy to technology.

Attendees are being pushed to provide those countries with more finance for infrastructure and technology projects, according to the foreign office.

G7 countries and their allies must offer "an alternative to unsustainable debt from non-market economies" like China, it said.

Ministers from the Association of Southeast Asian Nations (ASEAN) will join the G7 summit for the first time ever on Sunday, in a session earmarked for wide-ranging talks on issues including Covid-19 vaccines, finance and gender equality.

South Korea, Australia, South Africa and India will also participate as Britain's chosen G7 "guests", with many attendees taking part virtually due to the pandemic and emergence of the Omicron variant.

Truss said she wants deeper ties between G7 nations in trade, investment, technology and security to "defend and advance freedom and democracy across the world".

She will also unveil a UK-led initiative to boost collaboration investing in Africa's "most fragile markets" and help develop "a pipeline of investable opportunities".