Sen. Sam Brownback, R-Kan., on Thursday said he would do everything he can to hold up confirmation of President Barack Obama’s nominee to be Iraq’s ambassador, Chris Hill, a former assistant secretary of state for East Asian affairs.

Brownback and four other Republican senators earlier this week sent a letter to the administration about their opposition to Hill being nominated for the post, which has been vacant since Ryan Crocker left in January.

Brownback has said Hill would need a “crash course in Iraqi affairs.” He also criticized Hill’s involvement in six-party talks about North Korea’s nuclear disarmament, mainly for not making human rights a major issue in the talks.