A major U.S. newspaper is reporting that Iran has routinely switched off satellite tracking systems on its sea-bound oil tankers in a bid to sidestep international sanctions due to its controversial nuclear program. The news comes as Iran is set to meet U.N. nuclear agency officials.

The Washington Post quotes unnamed U.S. officials Monday saying Iran started the tactic in early April. The newspaper also reports that the Iranian practice – a violation maritime law – is being closely monitored by the International Atomic Energy Agency.

Switching off the tracking system has only been modestly effective in hiding the massive tankers.

Iran relies on oil exports for the majority of its foreign currency earnings. U.S. officials say the sanctions are drastically hurting Iran's economy, and the value of Iran's currency has dropped sharply.

Meanwhile, U.N. nuclear agency officials are expected to press Iran for access to the Parchin military site near Tehran. Iran has not yet granted U.N. requests to visit the site, where U.N. officials suspect Iran has built a container for explosives tests.

Western diplomats say they suspect Iran is buying time to remove any incriminating evidence from the site before they allow U.N. inspectors inside the facility.

Iranian officials meet with the IAEA Monday in Vienna, ahead of talks between Tehran and the five permanent members of the U.N. Security Council plus Germany in Baghdad on May 23. The six world powers, known as the P5+1, are seeking to assess the possible military capability of Iran's nuclear sites.

Western powers suspect Iran is developing nuclear weapons under cover of a civilian energy program, a charge Tehran denies.

Iran and the six world powers resumed talks on the dispute last month in Istanbul after a more than year-long stalemate.