PHOENIX -- The D-backs submitted an offer to Japanese free agent pitcher Hiroki Kuroda 10 days ago, general manager Josh Byrnes confirmed on Tuesday.

"I'm not going to comment on specifics," Byrnes said when asked about Arizona's offer. "He's someone at least back to last August that we started a file of reports on. When I was in Boston [as assistant GM] he was a guy that we looked at."

The 32-year-old Kuroda has pitched for 11 seasons for the Hiroshima Carp of the Central League where he compiled a 103-89 record and a 3.69 ERA. Last season in 26 starts for Hiroshima he was 12-8 with a 3.56 ERA.

A right-hander, Kuroda reportedly has a fastball in the mid-90s as well as a slider and forkball.

Kuroda would help the D-backs fill their biggest need this offseason. Arizona is looking to acquire at least one pitcher to go in the rotation behind Brandon Webb, Doug Davis and, hopefully, a healthy Randy Johnson.

The Mariners have been hot on Kuroda's trail for a while now and are thought to be the frontrunners, but Byrnes declined to comment on that or his team's chances.

"We'll just have to see," Byrnes said. "I think during the Winter Meetings we'll be communicating more."

A four-year contract that Kurodo signed with Hiroshima prior to last year included a provision that allowed him to file for free agency following the 2007 season, which he did. That means that a Major League team will not need to pay a posting fee to sign him and that Kurodo is free to sign with any team he wants.

Some reports have indicated that Kurodo is expected to receive at least $10 million a season in a deal.