While the U.S. ratchets up pressure on Iran to abandon pursuit of nuclear weapons, the Washington Post reveals that David Plouffe, one of Obama´s most senior advisers, accepted a speaking fee from MTN, the parent company of Irancell — a government-linked telecommunications operator in Iran.

While the Obama administration is ratcheting up pressure on Iran and tightening sanctions in efforts to curb Tehran´s nuclear ambitions, one of U.S. President Barack Obama´s most senior aides was paid $100,000 by a company doing business with Iran just before joining the White House staff, The Washington Post reported on Monday, raising tough election-year questions.

White House senior adviser David Plouffe received the speaking fee from Africa´s largest wireless phone operator, MTN Group, for two speeches he made in Nigeria in December 2010, the company and administration officials confirmed.

Plouffe listed the fee, alongside many others, on his official financial disclosures after he joined the White House in January 2011. An MTN subsidiary is a major shareholder in Irancell, a government-connected telecommunications operator in Iran.

While there has been no suggestion that Plouffe violated any law or regulation, the report has exposed the White House to attack from Republican opponents.

Plouffe managed Obama´s 2008 presidential campaign and has been an important behind-the-scenes player in the 2012 race, where White House efforts to curtail Iran´s nuclear program have come under fire from Republican contender Mitt Romney.

It is typical for Washington insiders to collect lucrative speaking fees between and after their government assignments. But Republicans said MTN´s work in Iran through Irancell made the Nigeria speeches bad choices.

"Today´s story raises serious questions," said Kirsten Kukowski, a spokeswoman for the Republican National Committee. "David Plouffe may be the biggest loophole in the international community´s sanctions against Iran."

Obama campaign spokesman Ben LaBolt responded by saying that Romney had an Iran problem of his own: he was late in fulfilling a pledge to divest in companies doing business with Iran, including a competing cellular company, Turkcell.

According to Romney´s financial disclosure statement filed in August 2011, the former Massachusetts governor sold his Turkcell investment in 2010.

White House spokesman Eric Schultz said Plouffe spoke to MTN about mobile technology and digital communications unrelated to Iran and did not meet separately with the company´s leadership.

"At the time, not even the most zealous watchdog group on this issue had targeted the Iranian business interests of the host´s holding company. Criticizing Mr. Plouffe now for issues and controversies that developed only years later is simply misplaced," he said.

MTN has denied violating any sanctions related to Iran, where according to the company´s website it has nearly 35 million subscribers.

MTN spokesman Paul Norman said Plouffe was invited to speak "because of his expertise and his knowledge of the U.S. political scene."

"It had no connection or relevance to Iran, and nor did Iran nor Turkcell form part of any discussions held," he said in an email to Reuters, referring to the Turkish cellphone company that has sued MTN over allegations the South African company used bribes to beat it out in Iran. MTN has asked for the case to be thrown out.

Obama has been tightening sanctions against Iran, along with the European Union and other partners, to choke off funds for its nuclear program that Tehran says is for peaceful purposes and Israel and others say is meant to develop weapons.