The shooting provided new ammunition to critics of Italian Prime Minister Silvio Berlusconi who have long attacked his close ties with Libyan leader Muammar Gaddafi and a deal with Tripoli to curb the flow of illegal African migrants into Italy.

The incident occurred on Sunday when a Libyan patrol boat — one of six Italy donated to Tripoli as part of the deal — fired with machine guns on a Sicilian boat with 10 men on board about 30 miles off the Libyan coast, according to Italian officials. Italian Interior Minister Roberto Maroni acknowledged the shooting should have been avoided and called it a serious incident, but blamed it on a mistake. He said he had ordered a probe.

“What happened the other day is something that should not have happened and Libya has apologized,” he told Italian TV. “Apparently there was an error of interpretation. Perhaps they mistook the fishing boat for a boat with illegal migrants. It was a serious incident, but just an incident nevertheless.”

Opposition politicians, who have joined human rights groups to denounce Libya’s treatment of illegal migrants intercepted on their way to Italy, said the motive remained unacceptable.

“The fact that the Libyan patrol fired because it mistook the Italian boat for a ship of migrants does not make it any less serious,” center-left Democratic Party senator Giuseppe Lumia said. “Here it’s a question of respect for international norms and fundamental human rights.” None of the fishermen was wounded, but the boat’s captain recounted to Italian newspapers moments of terror as bullets ricocheted around the crew and said they were lucky to be alive.

“It was an inferno and for a few minutes we didn’t know what was going on,” Gaspare Marrone told the Corriere della Sera daily. “I told my crew to throw themselves on the ground but the bullets were bouncing off all over and I feared someone would be wounded. They even hit gas canisters. It could have been a massacre but luckily we got away.”

Italian opposition politicians seized on the shooting incident to attack Berlusconi’s close relationship with Gaddafi, calling it the latest Libyan affront to Italy and demanded the government address the issue in parliament.