Belgrade airport security service has discovered two Hellfire missiles on an Air Serbia passenger flight heading from Lebanon to the US. The munitions, packed in wooden crates, were found by bomb-sniffing dogs. Serbian officials are investigating the incident, a source at the prosecutor's office told Reuters on Monday. Air Serbia has said it is helping with the probe. The shipment was accompanied by proper documentation and would have passed unnoticed, but for the dogs which sniffed out the explosives, local media reported. "Experts are determining whether the missiles were equipped with live or training warheads ... They were packed in proper transportation crates and supplied with paperwork which is also being scrutinised," a source close to the investigation told Reuters. According to the same source, the Lebanese and US authorities were aware of the shipment and ensured that the missiles posed no threat to the public. The rockets arrived on an Air Serbia flight from Beirut to Belgrade Nikola Tesla Airport on Saturday. They were to be transported to Portland, Oregon.