Standard Chartered has warned that it faces fresh fines from the US authorities for breaches of money laundering rules as it posted a 20% fall in first-half profits.

Two years ago the Asian-focused bank was fined $667m (£396m) for scheming with Iran to hide billions of pounds of transactions from the US authorities. It said new issues have now arisen which could lead to fresh penalties from the New York State department of financial services (NYSDFS).

The revelations about additional penalties and the possible extension of a two-year deferred prosecution agreement with the US authorities – which have installed a monitor in the bank – could put fresh pressure on the chief executive, Peter Sands, who said that the first-half results were "clearly disappointing".

Difficult conditions in its Korean operations and its financial markets operations were behind the 20% fall in profits to $3.2bn, a fall which the once fast growing emerging markets bank had flagged in June.

In legal warnings attached to its first-half results, the bank said: "Certain issues have been identified with respect to the group's post-transaction surveillance system, which is part of its anti money laundering systems and controls and is separate from the group's sanctions screening systems. The group is engaged in discussions with NYSDFS and the monitor with respect to those issues and their ongoing remediation."

It added: "The group believes that the resolution of these issues is likely to involve an enforcement action by the NYSDFS that would include an extension of the term of the monitor beyond the original two-year term, a monetary penalty and remedial actions."

Echoing remarks by the HSBC chairman, Douglas Flint, earlier this week, Standard Chartered also warned of the impact of a fresh flux of regulations hitting the banking industry. "The intensity of regulatory pressure and political risk, at a time of market weakness, is putting huge pressure on bank boards and management leadership generally," Sir Jon Peace, Standard Chartered's chairman, said.

"Whilst our first-half performance is clearly not as good as in previous periods, we have taken assertive action to manage short-term performance issues, and to position the group to take advantage of considerable long-term growth opportunities we see across our markets," Peace said.

Last month, the Standard Chartered board issued a statement backing the management teamafter reports that shareholders wanted change at the top of a bank that had previously reported 10 years of rising profits.