BP PLC (BP) said Thursday it is conducting an internal investigation into allegations of bribery at its tanker chartering division, after a letter detailing alleged corruption was sent to its chief executive last week.

The allegations, which center on the relationship between a senior BP employee and one of the company's suppliers, are contained in a letter sent to CEO Bob Dudley and the Serious Fraud Office, a copy of which was seen by
U.K. newspaper The Daily Telegraph and reported in its Thursday edition.

"We can confirm that the chief executive's office did receive a letter--as described--last week," said BP spokesman Robert Wine. "BP conducts its business to the highest ethical standards. We take all allegations of this sort extremely seriously and always investigate them."

BP declined to give any further details of the allegations.

According to the newspaper report, the central claim concerns the alleged chartering of tankers at preferential terms for the supplier in return for cash payments to the senior BP employee.

The author of the letter, a self-described "BP employee," offers to supply further evidence to back up the claims but only after the company launches an investigation.

A Serious Fraud Office spokesman wasn't immediately able to confirm whether the agency had received the letter or whether it had begun its own probe of the alleged corruption.