Bolivian President Carlos Mesa has handed in his resignation, a day after making a surprise announcement that he would quit.
About 1,000 supporters gathered outside the presidential palace
"I cannot continue to govern with threats that strangle the country," he said after a rash of protests during his 17 months in office.
If Congress accepts the resignation, Bolivia will have lost two presidents in less than two years.
Opponents dismissed Mr Mesa's action as a political ploy to stay in power.
Bolivia's constitution means Mr Mesa can keep his job if Congress rejects his resignation.
The legislature is expected to consider the resignation on Tuesday, and it is not clear what they will decide.
Mr Mesa is a political independent with no party backing.
His resignation marks the country's most serious political crisis since Mr Mesa took office, BBC South America correspondent Elliott Gotkine says.
Mr Mesa announced in a nationally broadcast address on Sunday he had "reached a limit".
In his resignation speech, he said his period in office had been blighted by no fewer than 820 protests.
Carlos Mesa has approval ratings between 50% and 60%
The latest nationwide protest, aimed at forcing changes in rules governing Bolivia's vast natural gas resources and due to take place over the coming days, would force the country to its knees, he said.
"In the next hours, the country could be completely blocked off," he said in his address.
A prominent opposition leader, Evo Morales, told the BBC that Mr Mesa was trying to blackmail the country to avoid change.
Mr Morales has promoted a bill that would increase taxes on foreign oil companies to up to 50% - a measure that Mr Mesa says would alienate foreign investors.
In a show of popular support for the president, some 1,000 people gathered beneath the balcony of the presidential palace in La Paz and urged Mr Mesa to reconsider his decision.
His national approval ratings run between 50% and 60%, our correspondent says.
Mr Mesa has also faced anger from the Santa Cruz region - home to some of the country's most important oil, sugar and soyabean companies.
The region accounts for 33% of the country's economic output.
In January, Mr Mesa said he would try to find a compromise to allow Santa Cruz residents to choose their governor without having to amend the constitution.
But local business and political leaders say they are receiving too little from the central government in return for the region's economic contribution to the state coffers.
If Congress accepts Mr Mesa's resignation, Senate President Hormando Vaca Diez would be his successor, since there is currently no vice-president.
Mr Mesa took over after his predecessor, Gonzalo Sanchez de Lozada, fled the country over nationwide protests in October 2003.
Mr Sanchez de Lozada and his cabinet are facing charges of genocide over the deaths of at least 60 people in protests.
The former president denies allowing his security forces to use violence against demonstrators.