The United Kingdom's Serious Fraud Office has requested documents from GlaxoSmithKline and AstraZeneca as part of an investigation into the United Nations' oil-for-food program.

The program allowed Iraq, which in 1990 was hit with international trade sanctions following its 1990 invasion of Kuwait, to sell oil for food, drugs and other basic items. The program involved more than 2,000 companies and ended in 2003.

The United Kingdom's fraud office is looking into allegations of kickbacks or bribes paid to Iraqi officials.

GlaxoSmithKline issued a statement Sunday that read: "During the time of the UN sanctions against Iraq GSK, along with most other pharmaceutical companies, took part in the UN program under which food and medicines could be supplied to Iraq in exchange for UN administered funding from Iraqi sales of oil.

"GSK does not believe that its employees or its agents in Iraq knowingly engaged in wrongdoing regarding the oil-for-food program. In fact GSK went to considerable lengths to cooperate with UK government authorities responsible for the UK administration of the program, and to impose anti-corruption measures when dealing with intermediaries in Iraq at a time when the environment was extremely volatile and difficult.

"GSK is cooperating fully and freely with the enquiries being made by the SEC and the SFO. Given that the investigations are continuing we do not consider it appropriate to comment further at this stage."

AstraZeneca officials said the company was fully cooperating with the investigation and conducted an internal investigation into the matter that found no unethical behavior by the company in its business dealings with Iraq.

Both companies are based in London. GlaxoSmithKline has a U.S. headquarters in Philadelphia. AstraZeneca's U.S. headquarters are in Wilmington, Del.