Two U.S. soldiers deployed to Kosovo spotted smugglers from Serbia trying to bring something over the border.

The goods they were trying to smuggle turned out to be $11,000 in alcohol, Army officials said Monday.

The soldiers, serving with the NATO peacekeeping mission, were on duty and watching the boundary line between Serbia and Kosovo, according to a report in Stars and Stripes.

They noticed two suspicious vehicles.

“Two of my soldiers called ... and informed me that there was a white van and a blue truck sitting on the Serbian side of the (border) and what looked to be people passing goods between the vehicles,” said Staff Sgt. Adam Kiefaber of the 61st Cavalry Regiment, 2nd Infantry Brigade Combat Team, 4th Infantry Division said in the report.

When the smugglers drove back into Kosovo, the soldiers knew something was up. No one should be crossing the border at that location, and there are designated checkpoint gates for people to use instead.

The soldiers alerted the Kosovo border police, who tracked down the vehicles.

The smugglers were trying to get the alcohol from Serbia into Kosovo without paying the appropriate customs duties, police said.

Smugglers attempt to bring all sort of items into the country including drugs, weapons and commercial goods, the Army said in a statement.