WASHINGTON (Reuters) - The US Justice Department is making inquiries into allegations of foreign exchange rate manipulation centred on the Swiss franc but has left the heavy lifting to Europe, according to a source familiar with the probe.

The Justice Department spoke with participants in the probe but is letting officials in Europe take the lead in any investigation, said the source, who could not be named to protect business relationships.

Two traders from an unnamed Swiss bank have been let go in connection with the allegations, said the source.

Investigations into the US$5 trillion (S$6.2 trillion)-a-day market have broadened, with authorities in Switzerland and Britain looking into whether traders at banks sought to manipulate benchmark foreign currency rates.