Ahern is in Washington for talks with President Bush and other lawmakers regarding a series of issues, including immigration policy and support for completing the Northern Ireland peace process.

The Prime Minister said he had asked Bush for a little more transparency regarding the payload aboard the flights that land and take off from Shannon airport.

"We have CIA flights that land, I'm sure, they're all on totally legitimate business. But, if at times we were able to say what some of these flights are about, all of these flights were about, then it would make an easier position for us and I think it would make public opinion happier on that.”

The British government has acknowledged in recent months that several private planes had landed at British military airports and had visited destinations in neighboring Ireland.

The U.S. is embroiled in rows with several countries over the use of airspace and facilities for extraordinary rendition - a process in which "terror" suspects are transferred from the U.S. to countries in which torture is known to occur.

U.S. Secretary of State Condoleezza Rice last December denied that suspects are tortured in third countries.