Three directors of engineering firm Alstom have been arrested in a corruption investigation, which saw raids on addresses in Warwickshire, Staffordshire and Shropshire, the Serious Fraud Office (SFO) said.
The men, aged 52, 51, and 44, are being questioned after a series of raids on offices and homes across England, including the West Midlands.
They have been arrested on suspicion of bribery and corruption, conspiracy to pay bribes, money laundering and false accounting. Other raids took place at addresses in Leicestershire, Cheshire, Derbyshire and London.
The investigation centres on suspected bribes paid in the UK to influence the awarding of overseas contracts to companies in the Alstom group.
Police offices from several UK forces and the Swiss Federal Police have been involved in the investigation.
SFO director Richard Alderman said: "The SFO is committed to tackling corruption. We are working closely with other criminal justice organisations across the world and are taking steps to encourage companies to report any suspicions of corruption, either within their own business or by other companies or individuals."