The world's big powers are debating whether to increase pressure on Tehran's nuclear programme by targeting Bank Sepah, a leading Iranian bank, with United Nations sanctions.

Such a move, against Iran's oldest bank, would follow a campaign by the US to persuade European nations to follow its example and take steps against Sepah that would exclude it from international markets.

In January, Washington barred US banks from doing business with Sepah because of what the Bush administration said was the institution's connections with Iran's missile programme. The decision effectively stopped Sepah from carrying out dollar transactions.

But moves in other jurisdictions would have a greater effect. Bank Sepah's wholly owned subsidiary Bank Sepah International claims it has "relationships in over 45 countries worldwide", as well as offices in London, Paris, Frankfurt and Rome.

To date, European Union countries have resisted taking action against Sepah, despite a campaign waged by Robert Kimmitt, deputy US treasury secretary, and Stuart Levey, Treasury under secretary for terrorism and financial intelligence.

States such as Germany and Sweden say that imposing measures against the bank would be legally difficult unless Sepah is specifically named by a UN Security Council resolution.

Unfounded allegations

Bank Sepah denounces what it says are Washington's "fabricated statements and unfounded allegations", adding that it "will spare no effort to seek righteous remedies in the near future".

Yesterday, European diplomats said they were discussing whether to include measures against Bank Sepah in a new resolution.

The issue will be addressed by diplomats from the permanent five members of the Security Council and Germany, who are due to discuss possible Iran sanctions today.The diplomats said no decision had yet been made about Sepah. But, in line with the policy of exercising incremental pressure on Tehran, which missed a deadline to curb its nuclear programme last week, the US and the EU want to strengthen measures set out by a previous resolution agreed last December.

Missile programme

That resolution targeted seven organisations the UN said were involved in Iran's nuclear programme, three involved in its missile programme, and 12 people connected with either or both programmes.

As well as adding new names to the lists, the EU and US want a new resolution to impose a travel ban on the people identified in the previous measure.

In addition, the six countries are discussing whether to impose limited restrictions on arms dealings with Iran - a measure Russia is very likely to resist - and whether to include language that would deter countries from subsidising trade with Iran.