NATO warships and helicopters pursued Somali pirates for seven hours after they attacked a Norwegian tanker, NATO spokesmen said Sunday, and the high-speed chase only ended when warning shots were fired at the pirates' skiff. Seven pirates attempted to attack the Norwegian-flagged MV Front Ardenne late Saturday but fled after crew took evasive maneuvers and alerted warships in the area, said Portuguese Lt. Cmdr. Alexandre Santos Fernandes, aboard a warship in the Gulf of Aden, and Cmdr. Chris Davies, of NATO's maritime headquarters in England. "How the attack was thwarted is unclear, it appears to have been the actions of the tanker," Davies said. Fernandes said no shots were fired at the tanker. Davies said the pirates sailed into the path of the Canadian warship Winnipeg, which was escorting a World Food Program delivery ship through the Gulf of Aden. The American ship USS Halyburton was also in the area and joined the chase.