By Mike Stone WASHINGTON (Reuters) – The U.S. State Department has approved the potential sale of HIMARS rocket systems to Estonia, missiles to Norway and torpedoes to South Korea in separate deals that could be worth more than $1.5 billion in all, the Pentagon said on Friday. The sales comes as European countries increase arms purchases after Russia invaded Ukraine, heightening security fears across the region. HIMARS systems donated by the United States and allies are being employed by Ukraine in its fight with Russia. The package approved for Estonia would include up to six M142 High Mobili…