* Serious Fraud Office says opened criminal probe
* Regulators around world investigating allegations (Adds details, background)
LONDON, July 21 Britain's anti-fraud agency said on Monday it has launched a criminal investigation into alleged rigging of the $5.3 trillion-a-day currency market.
"The director of the Serious Fraud Office has today opened a criminal investigation into allegations of fraudulent conduct in the foreign exchange market," the agency said in a statement.
Around 15 authorities around the world are investigating allegations of collusion and price manipulation in the largely unregulated foreign exchange market.
It is alleged that traders used online chatrooms to collude in the fixing of benchmark prices.
Scrutiny is focused on activity around London's 4 p.m. currency fix, a 60-second window where key exchange rates are set. These prices are used as reference rates for trillions of dollars of investment and trade globally.
Banks including Deutsche Bank, Lloyds, Citigroup, Barclays and JP Morgan Chase have fired or suspended - and in some cases reinstated - foreign exchange traders in the discourse over alleged manipulation.
Britain's financial regulator, the Financial Conduct Authority, launched its probe last October and the Bank of England in March appointed barrister Anthony Grabiner to examine whether any of its officials were involved in forex rigging.
The United States Department of Justice opened a criminal probe into the matter last October. (Reporting by Clare Hutchison. Editing by Steve Slater/Jeremy Gaunt)