"As of 24 Jan 2012, all new fixtures involving Iran and all carriages of products with Iranian origin have been suspended," said Henrik Ramskov, chief operating officer with Maersk Tankers, a unit of the Maersk group and one of the world's top tanker operators.
"Existing spot fixtures, single voyages, concluded prior to 23 Jan 2012 and other obligations entered into before 23 Jan 2012 will also continue to be performed within the framework of the exemption set out in the decision of the EU Council," he said.
The EU on Jan 23 banned imports of oil from Iran. European oil companies will be forced to sever all dealings in Iran crude by July.
The EU also agreed to freeze the assets of Iran's central bank and ban trade in gold and other precious metals with the bank and state bodies.
"The further EU sanctions on Iran contain an unprecedented package of prohibitions on the import, purchase and transport of Iranian oil that will affect our members trading patterns," said
Michele White, general counsel with INTERTANKO, an organisation whose members own the majority of the world's tanker fleet.
"This is now a highly restrictive and volatile environment in which we feel our members cannot trade without risk of breaching EU or indeed the myriad of other sanctions against Iran imposed by the U.S. and elsewhere."
A Maersk spokesman said its tanker unit made 14 Iran related voyages in 2011, "representing a miniscule part of their activity".
Iran is under increasing trade presure over its disputed nuclear programme and is facing further sanctions by the West.
The chief executive of Frontline, the world's largest independent tanker operator, told Reuters in December it did not have dealings with Iran.
New U.S. financial sanctions imposed since the beginning of this year to punish Tehran over its nuclear programme are playing havoc with Iran's ability to buy imports and receive payment for its oil exports, commodities traders said.