"It is a very important thing, but I can’t tell you why we stopped them," the officer said.
The US military personnel had undeclared M16 assault rifles and pistols concealed in their travel bags, Austrian media reported. They did not have permits to carry weapons.
According to the police source, several soldiers were on a journey from Rome to Ukraine.
"They did not arrive on time to the airport and the airplane had already left," he explained.
They were detained and put on a flight destined for Washington, together with their weapons.
Washington has backed Ukraine in its fight against independence supporters in the country’s southeast, although it said that US support would be limited to training and non-lethal aid.