The US State Department has imposed sanctions on three companies under the Iran Sanctions Act for conducting business with Iran’s energy sector.

The three firms are China’s Zhuhai Zhenrong Company, Singapore-based energy trading firm Kuo Oil and the UAE’s FAL Oil Company, according to a 12 January statement.

The sanctions came days after US Treasury Secretary Tim Geithner visited China to urge its government to do more to put pressure on Iran.

The State Department says Zhenrong is the largest supplier of refined petroleum products to Iran, brokering the delivery of more than $500m-worth of gasoline between July 2010 and January 2011, with individual deals worth significantly more than the $1m threshold for sanctionable activities within a 12-month period.

Kuo Oil is also accused of providing more than $25m in refined petroleum products to Iran between late 2010 and early 2011. FAL Oil also provided $70m in refined petroleum products in late 2010.

All three companies will now be barred from receiving US export licences, US Export Import Bank financing and loans more than $10m from US financial institutions. It is unclear how much business any of the firms does with the US.

The US has been ramping up sanctions on Iran since strengthening sanctions in July 2010. In May last year, the State Department sanctioned seven firms their activities in the Iranian energy sector (MEED 25:5:11).