Attorney General Henry McMaster, worried about North Carolina plans to transfer millions of gallons of water from rivers flowing into South Carolina, has said for months he plans to sue the neighboring state.

His office said Tuesday it plans a "major announcement in the state's water war with North Carolina," but McMaster, contacted by The Associated Press, did not say exactly what he planned to say on Thursday.

"The plan, of course, has always been to go to the Supreme Court," he said. "That is what we have planned from the very beginning."

South Carolina opposes plans by the cities of Concord and Kannapolis to pump up to 10 million gallons a day from both the Catawba and Yadkin river basins, both of which cross the state line.

Both McMaster and Gov. Mark Sanford oppose the water transfer.

McMaster wrote North Carolina Attorney General Roy Cooper in December, saying residents who live near the Catawba and Wateree rivers in South Carolina have urged him to "take whatever legal action is necessary to protect South Carolina's interests and rights. We are preparing to do so."

In similar water disputes between states, the U.S. Supreme Court has appointed a special master to determine the facts in the case.

"If it is something that requires a fact-finding procedure, then the U.S. Supreme Court will appoint a master and that is generally, I think, a retired judge from the federal bench," McMaster said. "Typically, cases like this take a good bit of time."

McMaster has said he will ask the Supreme Court to take the water case and wants to force North Carolina to enter an interstate compact with South Carolina over water issues.

He has said the 1993 North Carolina law creating that state's approval process for water transfers violates the U.S. Constitution because one state can't directly affect another state.