Slaughter and May has secured a mandate advising Standard Chartered in relation to claims by the New York State Department of Financial Services (DFS) that the bank was involved in a $250bn (£160bn) money laundering scheme with the Iranian government.

The magic circle firm is advising the bank in the UK over allegations published by the DFS yesterday (6 August), which claim Standard Chartered violated US sanctions against Iran for almost 10 years. The DFS alleges that the bank "schemed with the Government of Iran and hid from regulators roughly 60,000 secret transactions, involving at least $250bn (£160bn), and reaping Standard Chartered hundreds of millions of dollars in fees".

According to US legal title The Am Law Daily Sullivan & Cromwell is advising Standard Chartered in the US, with Rodgin Cohen, the New York firm's senior chairman, leading the team.

UK-headquartered Standard Chartered has defended its position in a statement, pointing out that it voluntarily approached all relevant US agencies in January 2010 to inform them about a review of transactions relating to Iran between 2001-2007 and their compliance with US laws.

It said the DFS had not provided "a full and accurate picture of the facts" and that "well over 99.9% of the transactions relating to Iran complied with the U-turn regulations. The total value of transactions which did not follow the U-turn was under $14m (£8.9m)."

Slaughters has previously advised Standard Chartered on matters including large projects and finance transactions, with corporate partner Nilufer von Bismarck often taking the lead role. The firm was reappointed as one of six advisers to the bank's international legal panel in March 2011.

Confirmation of Slaughters' role comes after numerous firms have picked up mandates in relation to the Libor rate-rigging scandal, which emerged in June this year, with several financial institutions including Barclays accused of manipulating interest rates on lending between banks.

Clifford Chance is advising both Barclays and the Royal Bank of Scotland on the fallout, with a Chinese wall set up to avoid potential conflicts, while a number of other firms including Freshfields Bruckhaus Deringer and Morrison & Foerster have also been handed key advisory roles on the scandal.