Hong Kong protesters planned a fresh show of force with a major rally Friday after talks with the government dramatically collapsed, and as they won powerful new US backing in their campaign for free elections.

Crunch talks between protesters and Beijing-backed city officials were planned for Friday, but fell apart Thursday after the government pulled out, blaming student leaders for threatening to escalate demonstrations if their demands were not met.

The decision deepened the ongoing political crisis in the Asian financial hub, with no end in sight to mass rallies that have paralysed parts of the city for nearly two weeks.

Demonstrators are calling for Beijing to grant the former British colony full democracy and for the city's Chief Executive Leung Chun-ying to resign.

Under plans unveiled by China in August, Hong Kongers will be able to vote for Leung's successor in 2017, but only two to three vetted candidates will be allowed to stand -- something detractors have dismissed as a "fake democracy".

Although protester numbers have dwindled in recent days, the collapse of the talks has spurred pro-democracy activists to push for new mass rallies over the weekend, with thousands expected to gather at 7:30 pm (1130 GMT) Friday outside the city's government headquarters.

The call came as US legislators condemned China's human rights record in a damning annual report, making a highly critical and unusual rebuke over Hong Kong.

Senator Sherrod Brown, chairman of the Congressional-Executive Commission on China, also called on Obama to press Chinese President Xi Jinping directly on "issues like Hong Kong" when they meet next month in Beijing.

China has repeatedly warned against any foreign government interfering in events inside the former British colony, which it views as an entirely domestic issue.

Dangerous new phase

Analysts Friday warned that the collapse of the talks pushes the confrontation between democracy protesters and the government into a dangerous phase, with neither side willing to back down.

Sunny Lo, a political analyst at the Hong Kong Institute of Education, said the government was spooked by a promise from pro-democracy lawmakers Thursday to disrupt the workings of the government in the city's parliament, known locally as LegCo, in a show of support for protesters.

"This is not a good sign now. The temperature is rising both inside and outside LegCo," he told AFP.

"If (the) Occupy Central movement drags on for a few more weeks I'm afraid police action would be inevitable. It would just be a matter of time," he added.

But Michael DeGolyer, a professor at Hong Kong Baptist University, said a violent police reaction was unlikely given it could reinvigorate the protest movement.

"They're not going to do the martyrdom thing. That would be a completely unnecessary act of dominance," he said.

With patience among many Hong Kongers running out following days of disruption, pressure is mounting on both Leung and the protest leaders to solve the stalemate.

Leung's opponents were given a major boost this week when details emerged that he had kept secret large payments from an Australian company while he was in office.

The Beijing-backed chief executive has denied any wrongdoing, saying he was under no obligation to declare the earnings and that he did not work for any company while in office.

But opposition lawmakers have smelled blood, threatening to bring impeachment proceedings against him while the city's top prosecutor will probe the allegations after a complaint was lodged with Hong Kong's anti-corruption watchdog.

Observers say Leung's bosses in China show no signs of dropping their support for the embattled leader.

"For the time being, Beijing will continue to let him deal with the crisis," Surya Deva, a law professor at City University of Hong Kong told AFP.

"But if he messes it up further, his head could come into the firing line."