(Adds comment from U.S. State Department)
LIMA, Dec 20 (Reuters) - Peru's two vice presidents pledged their loyalty to center-right President Pedro Pablo Kuczynski on Wednesday, on the eve of a congressional vote that could remove him from office over allegations of graft that he denies.
Many of Kuczynski's supporters have accused Congress of trying to mount a legislative "coup" with its vote on Thursday. They say that if the president is ousted, both of his vice presidents should both resign, thus triggering new elections that could erase the opposition's majority in Congress.
Peru's constitution does not specify what kind of elections must be called if the president and two vice presidents cannot govern, but Peruvian constitutional lawyer Enrique Bernales said both presidential and legislative elections are required by legal precedent.
The prospect of early elections that could sweep anti-establishment candidates to power amid anger at elected officials over a graft scandal has worried investors in one of Latin America's most stable economies.
The crisis - the worst to grip Peru since its return to democracy at the turn off the century - prompted First Vice President Martin Vizcarra to return to Lima from Ottawa, where he has also been serving as Peru's ambassador to Canada.
"I profess all of my loyalty...to the president of the Republic," Vizcarra said, declining to tell journalists outside his home if he would resign if Kuczynski were forced out.
In a tweet, Second Vice President Mercedes Araoz also voiced her "loyalty and total support for Kuczynski," adding, "We continue to work as a team to move forward with the Social Revolution which the people democratically voted for."
Late on Sunday, Araoz had told Reuters that she would not resign and that she and Vizcarra were committed to governing through 2021.
The accusations against Kuczynski stem from the disclosure last week by Brazilian builder Odebrecht that it made payments totaling more than $4 million to a company owned by Kuczynski while he held senior government posts more than a decade ago and to a company headed by a close associate of his in following years.
Odebrecht has rocked Latin American politics since admitting to bribing officials across the region a year ago.
Kuczynski, a 79-year-old former Wall Street banker, had previously denied any ties with Odebrecht, and has since said there was nothing improper about the payments.
Odebrecht said the transfers did not appear to be part of its corrupt dealings with politicians that its jailed executives have been detailing to prosecutors.
Lawmakers from the opposition party Popular Force, which controls Congress, have slammed Kuczynski as a corrupt lobbyist and said he is "morally unfit" to govern.
Thousands of Peruvians marched in front of Congress to denounce what they deemed a legislative "coup" by Popular Force. Protesters waved banners that read "Close Congress!" and "no to corruption."
Popular Force emerged from the populist movement started in the 1990s by autocratic former president Alberto Fujimori, who is now in prison for graft and human rights crimes. Kuczynski defeated the Fujimori's daughter Keiko, the party's current leader, in last year's presidential election by a razor-thin margin.
Kuczynski has slammed the opposition for not giving him time to explain his ties to Odebrecht, pointing to Congress' move to start "presidential vacancy" proceedings just two days after they were revealed.
Kuczynski's party, Peruvians for Change, has called the bid to oust him a hasty attempt at a 'coup.'
The secretary-general of the Organization of American States, Luis Almagro, said on Wednesday that the bloc was sending a team to Peru to keep tabs on "the current political situation" at Kuczynski's request.
In a letter posted by Almagro on Twitter, Kuczynski said the opposition's actions constitute "an assault against democratic order and the legitimate exercise of power," the president wrote, asking the OAS to observe Thursday's vote.
Popular Force has denied any anti-democratic actions and said its efforts to remove Kuczynski and its parallel effort to oust the attorney general were well within the bounds of the constitution and part of their battle against corruption.
Popular Force lawmaker Hector Becerril said Kuczynski had lost the country's trust. "He lies to the country and he lies to Congress about not having any ties to Odebrecht," Becerril told journalists.
The United States, where Kuczynski once held citizenship, said it would continue to collaborate with Peru's government.
"Peru is a strong democracy, and we are confident that the Peruvian people and institutions will address this situation according to Peru's constitutional norms," the U.S. State Department's Bureau of Western Hemisphere Affairs said.
Kuczynski had once raised hopes that his decades of finance and public administration experience would usher in a new period of economic growth in the world's No.2 copper producer.
But in a sign of how the crisis has engulfed his government, Peru postponed its auction of a $2 billion copper project, scheduled for Wednesday, for February. (Reporting by Mitra Taj and Marco Aquino; Additional Reporting by Teresa Cespedes; Editing by Frances Kerry and Grant McCool)