Prime Minister Shinzo Abe is likely to be re-elected president of the ruling Liberal Democratic Party in September without opposition after the man seen as his greatest potential rival decided not to run, an LDP executive said Thursday.

Shigeru Ishiba, minister for regional revitalization, seen as the potential biggest rival in the race, has told people close to him that he will not run, the LDP official said.

"I am now doing the best I could do as a Cabinet minister of the Abe administration," said Ishiba during a regular news conference. "There is nothing more I have to say."