Labour leader David Shearer has belatedly added a United States' based bank account to his entry in the MPs' Register of Pecuniary Interests, saying he had forgotten to include it previously.

Mr Shearer said the US bank account was used for his salary from the United Nations, where he worked prior to becoming an MP, but he had forgotten to declare it in the register.

He had contacted the registrar, Dame Margaret Bazley, to include it as a late addition to his returns since he entered Parliament in 2009. He would not say how much was in the account. MPs need to disclose only accounts with more than $50,000 in them.

MPs are required to disclose all their financial interests in the register each year, including debts, assets such as property or shares, and gifts worth more than $500.