BUCHAREST, Romania — Swiss pharmaceuticals company Roche confirmed Friday it is being investigated by anti-corruption prosecutors looking for evidence that drug companies offered doctors vacations and other incentives in exchange for prescribing cancer drugs.

Roche Romania told The Associated Press it was "fully cooperating" with anti-graft prosecutors and would provide the requested information.

Authorities have refused to say which companies are being probed, but Romania Curata, a site that reports on corruption, said 11 companies have been targeted, including Roche Romania, GlaxoSmithKline Romania and Pfizer Romania.

Pfizer, which was not immediately available for comment, told daily Evenimentul Zilei that it respected the "highest international standards and compliance procedures," and was unaware of any investigation.

Some 61 homes and offices were searched in Bucharest and in the northwest of the country on Tuesday in a probe centered on a number of medical institutes and the way certain cancer medicines were purchased and prescribed, according to anti-corruption chief prosecutor Laura Codruta Kovesi.

A prosecutor, speaking only on condition of anonymity because an investigation is underway, said that vacations and other material perks offered from 2012 to 2015 were worth tens of millions of lei (millions of dollars).

The anti-fraud tax department said Friday a number of tourism agencies issued bills to pharma companies from 2013 to 2014 purportedly for medics traveling abroad. Some of the bills, to destinations including Las Vegas and Paris, were fictitious, enabling the companies to claim back the 24 per cent sales tax, a statement said.