Forty-five American lawmakers have urged the US government to boycott next month's G20 summit in Riyadh unless Saudi authorities address key human rights concerns, according to correspondence released Wednesday.

The letter from US Congress members to Secretary of State Mike Pompeo comes after European lawmakers passed a resolution this month calling for the European Union to downgrade its attendance at the summit, also over human rights.

The developments are a source of embarrassment for the kingdom, the current G20 president, as it gears up to host world leaders next month at what is widely seen as a crucial event for Saudi international diplomacy.

Among a suite of demands, Congress members called on Riyadh to release jailed activists including several women, end its military campaign in neighbouring Yemen and provide accountability for the 2018 murder of journalist Jamal Khashoggi in Istanbul.

"As the world's leading democracy and purveyor of human rights, our government should demand dramatic changes to Saudi Arabia's dismal record of human rights violations," said the letter, seen by AFP.

"Should the Saudi government fail to take immediate steps to address this record, we should withdraw from the Saudi-led G20 summit and commit to making human rights reforms a condition of all future dealings with Saudi Arabia's government."

Jan Schakowsky and Ilhan Omar, Democratic members of the US House of Representatives, were among the 45 lawmakers who signed the letter, which was supported by advocacy group Freedom Forward.

There was no immediate reaction from the Saudi government or Pompeo.

The administration of US President Donald Trump is a key ally and supporter of Crown Prince Mohammed bin Salman, Saudi Arabia's de facto ruler.

- 'Whitewashing' -

The letter comes as Riyadh on Wednesday began a two-day Women 20 (W20) conference, aimed at promoting gender equality, ahead of the G20 summit on November 21-22.

"The Saudi presidency of the G20 has given special attention to discussing policies related to women," Saudi Arabia's King Salman told the conference in a speech delivered by a minister.

"Saudi Arabia has embarked on an exceptional reform journey... to empower women."

But the virtual conference came under fire from human rights campaigners angered at the ongoing detention of several Saudi women activists, including Loujain al-Hathloul.

"While courageous women are subjected to torture for peaceful activities, the Saudi government seeks to assert itself on the international stage as a 'reforming' power," said the New York-based Human Rights Watch.

"W20 attendees should refuse to play a role in Saudi Arabia's whitewashing efforts, use their platform to speak up for Saudi women's rights champions, and advocate for the end of all discrimination against women," it said on Tuesday.

Saudi Arabia is the first Arab nation to host the G20 summit.

It had planned for a grand meeting that would showcase the ambitious modernisation drive of Prince Mohammed, whose international reputation was tarnished by Khashoggi's murder.

But the novel coronavirus pandemic has dampened those hopes, making a physical summit impossible, as the kingdom faces international backlash over human rights.

Sixty-five members of the European Parliament have also signed a letter calling for the EU to downgrade its attendance at the virtual G20 meeting.

A downgrade would imply Commission President Ursula von der Leyen and the president of the European Council, Charles Michel, will not take part in the summit if they heed the call of lawmakers.