PHOENIX (AP) The Arizona Diamondbacks are threatening to sue Maricopa County and leave downtown Phoenix unless their ballpark is upgraded.

In a letter to county officials Thursday, the Diamondbacks say the county has failed to make $187 million in repairs to the ballpark that opened in 1998 when Arizona joined the National League as an expansion franchise.

The letter also says if the Diamondbacks determine a retrofit of Chase Field isn't feasible and if the county doesn't grant permission for the team to look elsewhere, ''we will ask the court for all appropriate relief.''

County officials say taxpayers built the ballpark with $238 million in sales taxes.

They also say that according to its contract with the county that runs through 2028, the Diamondbacks are prohibited from trying to move until 2024.

The Diamondbacks cited annual reports that say the stadium district is responsible for funding capital needs and improvements.