* Singapore law firm asks for vessels to be arrested
* Bunker barges owned by Vermont UM Shipping
* Vessels seized on behalf of Maybank for unpaid debts - source (Updates to add responses from law firm, bank in 4th paragraph)
SINGAPORE, April 5 (Reuters) - Four marine refuelling barges owned and operated by Vermont UM Shipping Pte Ltd were seized in Singapore on Monday night, according to the website of Singapore's Supreme Court.
Singaporean law firm Rajah & Tann seized the vessels over unpaid claims on behalf of its client, Malayan Banking Berhad, or Maybank, said a source with direct knowledge of the matter who declined to be identified as the person is not authorised to speak to the media.
The source declined to specify the amount of the claims against Vermont UM Shipping.
Rajah & Tann did not respond to an emailed request for comment. Maybank also did not respond to an emailed request for comment.
The vessels - the Angel Sun, Angel Moon, Angel Star and Ansheng - were seized on Monday night, according to the Supreme Court website.
The barges for marine refuelling, also known as bunkering, range between 4,999 and 6,964 deadweight tonnes, according to shipping data in Thomson Reuters Eikon. The vessels are qualified to deliver marine fuel oil and are equipped with mass flow meters, according to the Maritime and Port Authority of Singapore (MPA).
Vermont UM Shipping did not respond when contacted for a comment on the seizure.
Vermont UM Bunkering Pte Ltd, a now defunct Singapore-based marine fuels supplier, is a shareholder of Vermont UM Shipping, according to documents from Singapore's Accounting and Corporate Regulatory Authority.
In April 2016, the MPA stripped Vermont UM Bunkering of its operating licenses after finding discrepancies and wrongful declarations in records kept on board its bunkering vessels.
In November of the following year, Vermont UM Bunkering and three of its executives were charged with cheating as part of a government crackdown on short deliveries of fuel to vessels.
In 2015, Vermont UM was ranked by the MPA as the 18th-largest marine fuel supplier in Singapore by volume.
In 2017, Singapore, the world's largest bunkering hub, became the first port to mandate the use of mass flow meters for marine fuel oil deliveries to boost transparency. (Reporting by Roslan Khasawneh; Editing by Christian Schmollinger)