A spokesman for U.S. energy company Exxon Mobil said it was keeping close tabs on evolving ties between the U.S. and Iranian governments.

Bloomberg news reported Exxon hired a lobbying company, the Nickels Group, formed by former Sen. Don Nickles, R-Okla. to monitor Iranian sanctions measures.

"We are not lobbying on Iran sanctions," Alan Jeffers, an Exxon spokesman, told Bloomberg. "We are monitoring activities related to Iran in the U.S. government."

Nickles served as Senate Whip and chairman of the Senate Committee on the Budget before leaving office in 2005. Bloomberg reports Exxon's work with the Nickles Group is the first time since 2010 it hired a lobbying firm to review issues with Iran.

The Iranian government in early May said representatives from the United States were among those expected to attend an international investment conference in Tehran. If sanctions are lifted, Iran can expect "the presence of major international U.S. oil and gas companies," an official in the Iranian Oil Ministry said.

The Iranian government is pressing for more sanctions relief from a framework agreement slated to take force in mid-2015.

Iranian Oil Minister Bijan Zangeneh said in early April the Islamic republic could return as a dominant force in the Organization of Petroleum Exporting Countries once the nuclear deal is formalized. Iran holds the third-largest proven oil reserves among OPEC member states, behind Venezuela and Saudi Arabia, respectively.

Iran is limited to around 1 million barrels of oil per day in exports under the terms of a November 2013 deal with international powers. Exports could double if all sanctions are released later this year.

Nickles was quoted by Bloomberg as saying his firm was not working directly on issues related to Iranian sanctions.

"We are not influencing or advocating in any way on Iran sanctions; our work with regard to Iran has involved only monitoring legislative activity in the U.S. Congress dealing with that sanctions regime," he said.