Sen. Antonio Trillanes IV has alleged Mayor Rodrigo Duterte kept more than 200 million pesos (US$4.2 million) in a joint bank account with his daughter that he did not declare publicly in 2014 as required by law.

Trillanes, who is running for vice president and is backing a rival candidate of Duterte, went to the Bank of the Philippine Islands and met with the mayor's lawyer but said the questioned account was not opened for scrutiny.

When Trillanes stepped out of the bank, some of the dozens of Duterte supporters yelled "liar" at him before he was whisked off by escorts in a van. Riot police stood by to maintain order in the business district where Trillanes' supporters also came, carrying posters that read: "We don't want corrupt candidates."

A large throng of journalists, TV cameramen and photographers stood outside the bank to await the outcome of the meeting between Trillanes and Duterte lawyer Salvador Panelo.

Panelo said the mayor authorized him to ask that the questioned account be opened to prove the allegations were false, but bank officials told him it would take seven days to study the request.

"I have no problem with that," Panelo said he told bank officials.

Trillanes made public a signed statement, where he named the informant who provided him documents showing Duterte's alleged secret bank accounts, including in the bank branch where he met Panelo on Monday. When an investigation by him and his staff showed that his informant's disclosures were credible, he said he decided to go public.

"I believe it is important for our people to know about the gross misrepresentation and pretensions perpetrated by Mayor Duterte that he is poor and he lives a simple life when ... he held bank accounts containing hundreds of millions, if not billions of pesos," he said in the statement.

Panelo described the documents the senator showed to back his allegations as "bogus."

Trillanes has said he would resign as a senator if his disclosure was wrong.

Duterte's spokesman initially denied last week the mayor had such a bank account. The mayor, however, acknowledged its existence on Friday in a news conference but denied he had committed any wrongdoing, although he did not explain where the money came from.

"I will admit there is money in that account," Duterte told reporters, saying it was less than the 211 million pesos that Trillanes had alleged.

The tough-talking Duterte has led voter preference polls ahead of the May 9 elections on a promise to eradicate crime and corruption in the country within six months if he triumphs.

It remains unclear whether the controversy over Duterte's bank account will affect his strong popularity with a week to go before the elections.

Duterte remained in the top spot in the most recent polls despite a storm of criticism after he remarked that he wished he could have been the first to rape an Australian missionary who was sexually assaulted and killed by inmates in a 1989 prison riot because she was so beautiful.

Questions over the mayor's unexplained wealth, however, go against his pledge to fight crime, which has won him wide support, analysts said.

Amid the controversy, two rival candidates, former Interior Secretary Mar Roxas and Sen. Grace Poe, separately said they have signed waivers allowing anti-graft officials to look into their bank accounts for transparency and challenged Duterte to do the same.

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Associated Press writer Teresa Cerojano contributed to this report.