Former President Bill Clinton was paid $2.5m (£1.6m, €2.3m) in speaking fees by major corporations and trade associations even as they lobbied his wife, Hillary, while she was US secretary of state.

An IBTimes US investigation revealed that the fees from 13 firms and trade bodies were paid directly to Mr Clinton and not to his philanthropic foundation. The companies included Microsoft, Oracle and Dell.

Many of the companies that paid Clinton for these speeches engaged him within the same three-month period in which they were also lobbying the state department in pursuit of their policy aims, federal disclosure documents show.

Several companies received millions of dollars in state department contracts while Hillary Clinton led the institution.

The situation has heightened the perception in the US that the corporate interests are able to influence government action by creatively funnelling money to those in power.

"The dynamic is insidious and endemic to this system," said Meredith McGhee, policy director of the Campaign Legal Centre, a campaign finance watchdog group in Washington.

"The fact is that the wealthiest .01% on the outside of government believes – fervently – that by paying speaking fees, or making campaign contributions, that it can gain access and influence."

Federal ethics rules aim to discourage officials and their spouses from accepting gifts from interests "seeking official action" from a government agency.

But the rules do not apply to speaking fees, said Craig Holman an advocate for tightened ethics structures at Public Citizen, a watchdog group in Washington.

"There isn't an ethics rule that prohibits someone like Bill Clinton from charging exorbitant speaking fees and collecting those speaking fees from businesses that have interests before the administration," Holman said.

Hillary Clinton

But despite this the dynamic through which President Clinton has been able to profit from the same companies eager to gain the ear of his wife's department "poses a very troubling conflict-of-interest situation that is going to continue to dog Hillary over the course of the campaign," Holman added.

The Clintons did not respond to IBTimes' questions about the propriety of the speaking arrangements. A spokesperson for the White House referred questions to the state department and the Clinton Foundation, neither of which responded.

The investigation revealed that 10 of the 13 firms that paid Bill Clinton speaking fees and lobbied the state department did so within the three-month reporting period.

Five technology firms – Oracle, Dell, Microsoft, SalesForce and VeriSign – collectively paid Bill Clinton a total of $1.05 million.

Microsoft and Oracle did not respond to questions but Dell spokesman David Frink said that the company regularly communicates with the US government and that Bill Clinton was asked to speak because of his "unique perspective on global affairs".

Bill Clinton also received $200,000 from the National Retail Federation in January 2012, during the same time period the group was lobbying the state department.

At that time, the trade association, which represents retail businesses, was opposing legislation to fight Chinese currency manipulation that could cost companies doing business there.

The group said its payments to Bill Clinton had nothing to do with its work lobbying the former president's wife.