UNITED NATIONS, Sep 20 (AFP) - Tensions rocked the Western alliance Monday (Sep 20) as European Union leaders backed France in its anger over a scuppered mega-contract, but US President Joe Biden addressed a key European grievance by easing COVID-19 travel restrictions.

The tensions in the transatlantic alliance overshadowed the beginning of the UN General Assembly week, with Biden hoping to turn the page on the turbulent presidency of Donald Trump and rally allies in the face of a rising China.

Biden, who will address the summit on Tuesday, is also seeking to step up action on fighting the pandemic and climate change, and forge global unity on Afghanistan, where the Taliban swiftly took control after he withdrew US troops last month.

But tensions with France suddenly took center stage after Australia last week cancelled a multi-billion-dollar contract for French submarines, instead opting for US nuclear-powered ones as part of a new three-way alliance with Washington and London.

European Council chief Charles Michel said the bloc would seek answers, saying that allies needed to be sure of "transparency and trust".

"We are observing a clear lack of transparency and loyalty," he told reporters.

With Trump, "at least it was really clear - the tone, the substance, the language - it was very clear that the EU was not in his opinion a useful partner, a useful ally", Michel said.

European Union foreign ministers, meeting in New York, "expressed clear solidarity with France", top EU diplomat Josep Borrell said.

"This announcement ran counter to calls for greater cooperation with the European Union in the Indo-Pacific," he said.

French Foreign Minister Jean-Yves Le Drian has accused the United States of betrayal and Australia of back-stabbing, and has no separate meeting scheduled with US Secretary of State Antony Blinken.

Le Drian called on Europeans to "think hard" about alliances, saying the contract showed "the persistence of reflexes from a time we had hoped had passed".

US officials noted that Blinken will see Le Drian in a group setting Wednesday during talks on Iran amid last-ditch efforts to salvage a 2015 nuclear accord.

Asked about a bilateral meeting, senior State Department official Erica Barks-Ruggles said that "the schedule will remain dynamic".

Biden also plans to speak by telephone with French President Emmanuel Macron, one of a number of leaders skipping the General Assembly due to COVID-19 precautions, on "the way forward", another official said.