The smoke alarms have led to accusations that Aer Rianta, which manages Shannon, is turning a blind eye to the smoking soldiers because the airport makes so much money from U.S. military landings.

In recent weeks, according to a report in the Irish Independent, the airport's automated fire alarm system has been activated several times, resulting in fire crews and security personnel rushing to investigate the source of the emergency.

And on at least six occasions, U.S. soldiers were found to be the culprits.

They were encamped in the bathrooms puffing away.

After one alarm, according to the report, the airport was evacuated when fire crews failed to locate the source of the emergency within the 10 minutes allowed before an automatic evacuation procedure kicked in.

All the alarms were triggered in a part of the terminal building where troops traveling to and from mostly the Middle East are segregated from regular civilian travelers.

Airport workers have complained that the troops should be held to the same non-smoking rules as everyone else.

But Aer Rianta has declined to say whether the smoking ban is under siege from the soldiers.

The Irish Independent reported that the management agency had refused to answer a list of questions regarding the smoking reports.

"Aer Rianta complies fully with the smoking legislation and will continue ensure that the smoking ban applies to all passengers, members of the public and staff members," Aer Rianta said in a statement. It did not elaborate.

The report pointed to "airport sources" citing fear that lucrative U.S. military business could be in jeopardy from the smoking ban as being a reason for Aer Rianta not taking the offensive against the breaches.

Ireland's smoking ban in public places is near absolute. But Frankfurt airport in Germany, another major transiting hub for U.S. military personnel and a clear alternative to Shannon, does not operate a blanket ban.

U.S. troops have been transiting through Shannon airport in increasing numbers in recent months.

A total of 16,697 military personnel on 161 flights passed through Shannon in March, Aer Rianta figures show. In all, 35,926 U.S. military personnel went though Shannon in the first three months of this year.

This is less than 10 percent below the same period last year when the U.S. military was building up for the invasion of Saddam Hussein's Iraq.

A total of 125,855 U.S. military personnel landed at Shannon last year. They came and went on over 1,500 flights that earned in excess of €15 million in revenue for Aer Rianta.

The use of Shannon by the U.S. military has been a controversial issue and has attracted protests from anti-war groups and others. But the Irish government has indicated that it has no plans to withdraw, or restrict, the use of the airport by the Pentagon.