Senate Republican opposition is mounting against President Obama’s choice to be the next U.S. ambassador to Iraq, Christopher Hill.

Following the GOP Conference meeting Tuesday, five senior senators sent a letter to Obama urging him to withdraw the nomination. They decried what they see as Hill’s lack of Middle East experience and his poor handling of the six-party talks on North Korea’s nuclear program.

“We do not believe that now is the time to appoint an ambassador who may need the equivalent of a crash course in Iraqi affairs,” the letter stated. “There are today, both within the Foreign Service and outside it, a number of individuals who possess much greater qualifications for this post than does” Hill.

Among the latest Republicans to come out against the nomination is Minority Whip Jon Kyl of Arizona, who said he couldn’t understand why Obama hadn’t chosen someone who speaks Arabic or has diplomatic experience in the region.

“This is arguably the most important ambassadorial position the U.S. has right now, and I’m sure there must be some other people who have spent any time whatsoever in the Middle East,” Kyl said in an interview. “I suggest they try to find somebody else.”

Kyl’s objections echo those of his Arizona colleague, Republican Sen. John McCain , who released a statement opposing the Hill nomination last week, along with Sen. Lindsey Graham , R-S.C.

Besides Kyl, the other signees were Sam Brownback of Kansas, James M. Inhofe of Oklahoma, John Ensign of Nevada and Christopher S. Bond of Missouri.

Hill did receive an endorsement from the Foreign Relations Committee’s ranking Republican, Richard G. Lugar of Indiana, meaning Hill’s nomination is likely to be approved in committee after his scheduled March 25 hearing.

“He has very good contacts in Iraq, and I’m convinced he has the experience to be an exemplary ambassador,” Lugar said after meeting with Hill. Lugar also praised Hill’s work in East Asia.

Brownback, who spearheaded the letter, said in an interview that he is considering placing a hold on the nomination. Such a move could stall action indefinitely.

In addition to his criticisms of Hill’s experience and qualifications, Brownback also questioned the nominee’s credibility with Congress, referring to promises Hill made to him regarding North Korea last year.

At a July hearing of the Senate Armed Services Committee, Hill, as the chief negotiator for the six-party talks, promised Brownback he would elevate the human rights issue in bilateral discussions and invite Jay Lefkowitz, the State Department’s special envoy for North Korean human rights, to all future negotiations with the North Koreans.

In exchange, Brownback lifted his hold on the nomination of Kathleen Stephens to become ambassador to South Korea. Neither promise was kept, Brownback said. “I had a direct statement made to me in open hearing and nothing happened,” he said.