Peruvian presidential candidate, Keiko Fujimori, is facing a storm over allegations that one of her closest confidantes laundered money for her in a previous election campaign.

The US Drug Enforcement Administration is reported to be investigating top Fujimorista politician and financier Joaquín Ramírez for allegedly cleaning $15 million for her previous, narrowly-failed presidential bid in 2011.

The US Spanish-language network Univision and Cuarto Poder, a Peruvian current affairs program, broadcast a film of DEA officials confirming the investigation on Sunday — with three weeks to go before this year's election.

Ramírez, 46, is secretary general of Fujimori's conservative Popular Force party. He was reelected to congress in the April 10 legislative and first round presidential elections.

He is also known to have contributed significant funds to the party although exactly how much is unclear; Popular Force has refused to publish its full party accounts.

A self-made millionaire who rose from humble beginnings collecting fares on crammed buses in Lima's chaotic transport system, Ramírez has never fully explained the source of his fortune.

The Univision-Cuarto Poder scoop revealed that the congressman owns two departments in Miami worth $3 million, neither of which he had declared in Peru.

New allegations emerged on Tuesday in the Peruvian paper La República. The paper claimed that Ramírez' is being investigated over links to Miguel Arévalo Ramírez, an alleged drug lord and the subject of a related DEA probe.

The DEA, which normally follows a strict policy of neither confirming nor denying when an investigation is under way, declined requests to comment about Ramírez, or why investigators had previously admitted on camera that the businessman-turned-politician is the target of a probe.

The agency has, however, ruled out a specific investigation of the presidential candidate herself.

"Keiko Fujimori is not currently, nor has been previously, under investigation by the DEA," the agency said in a one-sentence statement released on Monday that has done little to quell the scandal in Peru.

Both Ramírez and Keiko have denied any ties to drug money.

Keiko told reporters, while on the campaign trail in the highland city of Cusco on Monday, that the Univision report was part of a "dirty war" against her candidacy.

It is not clear what impact the allegations will have on the upcoming presidential poll in Peru, where corruption scandals are so common as to seem mundane, and many voters simply assume that a significant portion of their elected leaders are crooks.

That is partly thanks to the legacy of Keiko's father, Alberto Fujimori, who was Peru's hard-right president throughout the 1990s. He is now serving a 25-year jail term for massive corruption and human rights abuses.

Ahead of the June 5 runoff, his daughter is in a statistical tie with her center-right rival Pedro Pablo Kuczynski, a 77-year-old former prime minister.

Since winning the first round in April, Keiko has veered further to the right, reneging on previous commitments to recognize same-sex civil unions and allow abortion for rape victims.

Keiko has also signed deals with illegal miners to allow them to continue to ravage the Amazon, promised to reverse reforms of the corruption-plagued police, and met with a construction union leader who once served time for racketeering.

Former anti-corruption prosecutor Julio Arbizu said the allegations against Ramírez were a foretaste of bigger scandals to come should Keiko be elected president.

He said it was "inexplicable" she should continue to shield her ally against such grave accusations.

"He is not just being investigated by the DEA; Peruvian prosecutors have been investigating him for three years," he said. "I don't believe them when they say they have a plan to fight corruption. Fujimorismo would not just be permissive of graft. Many of its biggest names would actively be engaged in corruption."