Belgium-based SWIFT, which operates the bulk of global cross-border payments, said on Friday it was ready to implement sanctions against Iranian financial institutions as part of new U.S. and European restrictions against Tehran.

The Society for Worldwide Interbank Financial Telecommunication said it understood the European Union was drafting new international sanctions regulations directly affecting EU-based financial communication service providers.

SWIFT stands ready to act and discontinue its services to sanctioned Iranian financial institutions as soon as it has clarity on EU legislation currently being drafted, it said in an emailed statement.

SWIFT said it was also closely following the progress of a bill passed by the U.S. Senate's Banking Committee seeking to cut off Iranian financial institutions.

The United States accuses Iran of seeking to develop nuclear weapons and has been pressuring the European Union and SWIFT to expel Iranian banks from the network to deprive Tehran of funds.

SWIFT, whose headquarters are just outside the Belgian capital Brussels, is vital to international money flows, exchanging an average 18 million payment messages per day between banks and other financial institutions in 210 countries.

Expelling Iranian institutions from SWIFT would bar Iran from the principal avenue to transact with the rest of the world.

Nineteen banks and 25 connected institutions from Iran sent and received some 2 million messages in 2010. They included banks the U.S. accuses of financing Iran's nuclear programme or terrorism - Mellat, Post, Saderat and Sepah.

SWIFT, which was founded in 1973 and has never cut off a country before, said its decision reflected the extraordinary circumstances of multilateral international support for the intensification of sanctions against Iran.

SWIFT, which is overseen by the world's largest central banks, said it had informed them of its decision.

Belgium said on Thursday that SWIFT should not be the only company of its kind required to comply with sanctions.

(Reporting By Philip Blenkinsop; editing by Luke Baker)