Norway has asked Israel to explain the legal grounds for detaining a Norwegian-flagged fishing boat seized while activists tried to sail with aid to the Gaza Strip, Norways foreign ministry said on Tuesday. The ministry said its diplomats in Israel had been providing consular assistance to five Norwegians who were among the 22 passengers and crew detained onboard the vessel Kaarstein on Sunday. Two Israelis on board were quickly released. "We have asked the Israeli authorities to clarify the circumstances around the seizure of the vessel and the legal basis for the intervention," the spokesman for the Norwegian foreign affairs ministry in Oslo said. Torstein Dahle, head of the group Ship to Gaza Norway which organized the shipment, said it was the first Norwegian aid vessel to attempt to breach the Israeli blockade of Gaza. The captain had been struck on the head by Israeli soldiers who ordered him to sail for Israel, but no one was seriously hurt, Dahle said. "This is a peaceful boat; its impossible that it can threaten Israels security," he said. Numerous activist ships have been prevented from reaching Gaza in recent years.