MEXICO CITY (Reuters) - Mexico's president came under pressure on Friday to fully disclose his financial assets following a Reuters report on Thursday that he had misrepresented the circumstances under which he acquired a property in a lakeside retreat near Mexico City.

Opposition lawmakers from left and right called on President Enrique Pena Nieto to detail all of his properties, saying he had undermined his own efforts to battle corruption.

Meanwhile, legal experts and two former government officials tasked with overseeing public servants, said the assertion by Pena Nieto's office that the plot of land was donated by his father was inaccurate, if, as the public registry document seen by Reuters stated, he was named as sole purchaser.

"If he appears as the buyer, there's no way he can say it was a donation," said Elizabeth Yanez, a lawmaker from the center-right opposition National Action Party (PAN) and a member of the transparency committee in Mexico's lower house.

"He is falsifying," added Yanez, who formerly held one of the top posts in the Public Administration Ministry, an executive-branch watchdog known by the Spanish acronym SFP.

An official at the president's office declined to comment on the objections to how the property was described in the official document.

Reuters found that Pena Nieto bought a 1,000 square meter piece of land in the town of Valle de Bravo in 1988 from a third party, a property he had declared to authorities was donated.

The document showed that Pena Nieto directly purchased the property. There is no reference to his late father in the document.

Under Mexican law, even if his father gave him the money to purchase it with, he could not declare it as a donation, lawyers said, pointing to articles 7610 and 7620 of the Civil Code of the State of Mexico, the region where Valle de Bravo lies.

Pena Nieto lists five other properties as donations from his parents, but has given no details on where they are located.

The president has been under pressure in recent months over a series of conflict-of-interest scandals centered on properties that he, his wife Angelica Rivera and Finance Minister Luis Videgaray acquired from government contractors.

"These sorts of excesses, evidence of falsehood in his declaration of assets ... are incredibly serious," said Alejandro Encinas, a left-leaning senator and former Mexico City mayor, calling for all the assets to be properly disclosed.

The revelation over the land showed the presidency was undermining its own pledges to improve transparency, he added.

Mexican public officials face no requirement to publicly explain the source of any funds that were used to obtain properties they receive as gifts, but they are required to accurately declare how they acquire their properties.

Enrique Aubry, a congressman for the Green Party, allies of Pena Nieto's Institutional Revolutionary Party (PRI), defended the president, saying he had shown he meant to clean up politics by promulgating a new anti-corruption law this week.

Aubry argued that Pena Nieto's foes were trying to discredit the president before mid-term elections due on June 7.

"Because it's election time, they're trying to hurt the government," he said.

Prior to the report published on Thursday, the president's office had declined to give answers to various questions about differences between his declaration of assets and the document obtained by Reuters via a public information request.

Presidential spokesman Eduardo Sanchez posted a letter to Reuters correspondent Simon Gardner on the presidency's Website late on Thursday stating that Pena Nieto's father bought it and decided to put it in his son's name.

Several lawmakers responded to the Reuters report by saying the assets of all top officials should be made public.

In addition, Mexico needed to change the law to put an end to presidential immunity, said PAN senator Laura Rojas.

"If not, the number one public figure in the country will still be subject to exemptions," she said.

(Additional reporting by Mexico City newsroom; Editing by Kieran Murray)