Republican Eric Greitens' campaign for Missouri governor is accusing Democratic opponent Chris Koster of political gamesmanship, after Koster threatened to end negotiations for a debate unless Greitens releases his tax returns.

Koster's campaign sent a letter Tuesday to Greitens' campaign manager, Austin Chambers, noting that Koster released his own returns for the years 2012 through 2015. The letter says Greitens has promised to release his returns once Koster did so, but so far has not.

The letter calls on Greitens to release his personal returns and those for Eric Greitens LLC by Thursday. The letter says the release of taxes is an "absolute conditon" for continued discussion of a debate on Oct. 14.

In a response letter, Chambers says Koster is "terrified" of debating Greitens, and trying to "hide."