LONDON (Dow Jones)--Iranian oil stored at sea is building up due to international sanctions but the measures are also proving a boon to its home-grown tanker operator, officials in Tehran said Tuesday, underscoring the mixed effect of mounting pressure on the country.

  

National Iranian Tanker Company (NITC) plans a $1.2 billion expansion to its fleet as foreign tanker companies beckon off Iranian shipments in the wake of sanctions.

 

NITC's success is the latest example of how Iranian companies, often tied to Iranian power-brokers, are able to benefit from sanctions. After foreign companies pulled out from Iran's oil and gas projects, they were, in many cases, replaced by domestic contractors.

 

NITC has not been specifically sanctioned, although a U.S. congressman has recently drafted a bill to extend sanctions to the company, which is private.

 

Yet the restriction, are boosting demand for Iran's own tankers.

 

With many foreign shippers halting Iranian oil sailings due to banking and insurance sanctions, state-owned NIOC is increasingly relying on NITC.

 

"There are some difficulties for transportation" of Iranian oil, another Iranian official said. As a result, "there is more demand for NITC tankers" from NIOC, notably in Asia.

 

Indeed, NITC, one of the world's largest tankers operators, is set to boost its fleet with 12 new very large tankers, worth $1.2 billion in total, by the end of next year.

 

As a result of this expansion, NITC's tankers could cover about 40 percent of the country's crude exports compared to 30 percent today, the official added.

 

NITC's new head, Hamid Behbahani, who was appointed in January, is close to Iranian president Mahmoud Ahmadinejad, for whom he once served as transportation minister.

 

U.S. legislators, however, are trying to target this unforeseen impact of sanctions. A bill to sanction NITC was introduced late January by Howard Berman, a Democrat from California, at the U.S. House of Representatives, though it has yet to move beyond specialized committees.