North Charleston started the clock ticking faster in its fight over rail lines by issuing a mandatory 60-day notice that it intends to sue if the federal government doesn't stop South Carolina from building a rail terminal at the former Charleston Navy Yard.

Mayor Keith Summey said the suit is necessary because the state has showed no signs of altering its pursuit of rail through the northern end of the base, a path the mayor says violates an agreement signed years ago and would destroy years of neighborhood redevelopment.

"We've been pushed into this position by the state of South Carolina," Summey said Wednesday.

Unless a resolution that isn't "detrimental to the citizens of North Charleston" can be reached, the suit will be officially filed in 60 days, the city said. The venue will be federal court.

State officials were critical of the move, saying there is still an open window for compromise.

"It's unfortunate that the city feels like it must file a lawsuit, but that's the city's prerogative," said state Sen. Larry Grooms, R-Bonneau, of the state Port Oversight Commission.

A spokesperson for Gov. Nikki Haley referred the state's response to Commerce Department Secretary Bobby Hitt, who called the threat of legal action "unfortunate."

The Commerce Department supports a plan that allows rail use through the north and south ends of the city, which they contend ensures dual competitive access for both of the region's major rail lines carriers, CSX Transportation and Norfolk Southern.

"It is imperative that both Class I railroads have equal access with a balanced approach to the (proposed train transport operation) to help ensure the success and competitiveness of our port facilities," Hitt said in a press statement.

Summey said the suit has been explored for months, but is being activated now because the state has already started moving to condemn property needed for its rail plan.

The city is not seeking to halt any of the construction work now under way at the new terminal, which is slated to begin operating around 2018. Instead, Summey wants the original approving 2002 memorandum of understanding signed with the State Ports Authority, to be adhered to.

The memorandum "forbids cargo from the marine terminal being transported by rail across the northern end of the former Naval Base Property," city attorneys wrote in a letter outlining their case. That means preventing the commerce alternative, the city said.

Summey also had harsh words Wednesday for the ports authority, saying the body has taken "a coward's position" in not being more vocal against the state's rail ambitions.

SPA spokesman Byron Miller said the agency is holding up to its end of all agreements. "The Ports Authority is complying fully with its obligations under the MOU and will continue to do so," he said. "Allegations to the contrary are incorrect."

He added "we continue to say that South Carolina and businesses that use rail would benefit from a dual-access, regional rail solution that enjoys the support of both railroads."