Ashton Carter confers with Senate Armed Services Committee Chairman John McCain at his confirmation hearing on Feb. 4, 2015. (Jonathan Ernst/Reuters)

Defense Secretary Ashton Carter said Iraqi forces "showed no will to fight" as the Islamic State militant group captured the city of Ramadi, and he rejected calls by Republican lawmakers to commit ground troops to the conflict.

"What apparently happened was that the Iraqi forces just showed no will to fight," Carter said in a CNN interview that aired Sunday. "They were not outnumbered. In fact, they vastly outnumbered the opposing force, and yet they failed to fight. They withdrew from the site, and that says to me, and I think to most of us, that we have an issue with the will of the Iraqis to fight ISIL and defend themselves." The Islamic State is also known as ISIS or ISIL.

[Fall of Ramadi raises new questions about U.S. strategy in Iraq]

In an interview last week with the Atlantic, President Obama called the fall of Ramadi a "tactical setback" in the U.S. effort to defeat the Islamic State but said, "I don't think we're losing."

Those comments drew criticism from other officials who appeared on Sunday talk shows.

"We're losing. There's no doubt about it," John Bolton, the former U.S. ambassador to the United Nations, said on "Fox News Sunday."

Sen. John McCain (R-Ariz.), appearing on CBS's "Face the Nation," said the Obama administration has "no strategy" to defeat the Islamic State and said more troops needed to be sent to Iraq.

"We need to have a robust strategy. We need more troops on the ground. We need forward air controllers," McCain said. "But just referring to airstrikes, do you know that 75 percent of those combat missions return to base without having fired a weapon? It's because we don't have somebody on the ground who can identify  . . . a moving target."

Comparing the current situation in Iraq with the most difficult period during the Iraq war, McCain said: “George W. Bush at least had the guts to reverse and sponsor the surge, which eventually succeeded. I wish, I pray, that Barack Obama would do the same thing.”

But Carter said he was not prepared to recommend sending ground troops into Iraq and rejected critics who say U.S.-led coalition airstrikes against the Islamic State have not been effective.

"Airstrikes are effective, but neither they or anything we do can substitute for the Iraqi forces' will to fight," Carter said.

Obama has limited the role of the 3,000 U.S. troops in Iraq to providing training and technical assistance.

[U.S. advisers in Iraq stay out of combat but see fighting edging closer]

"We can give them training, we can give them equipment — we obviously can't give them the will to fight," Carter said. "But if we give them training, we give them equipment, and give them support, and give them some time, I hope they will develop the will to fight, because only if they fight can ISIL remain defeated."

Rep. Adam Schiff (Calif.), the ranking Democrat on the House Intelligence Committee, said on "Face the Nation" that the loss of Ramadi was "a serious setback" but that "sending in our own troops is not the answer."

Schiff echoed the sentiments of Obama and supporters of limited military involvement, arguing that the real issue in Iraq is continued sectarian divisions and the Iraqi government's failure to fully incorporate the Sunnis.

"We won Ramadi, but it didn't stay won, because of all the political problems," Schiff said. “I think we still have a lot of work to get the Iraqi government to peel the Sunnis away from ISIS.”

He said that instead of sending more troops, which could inflame tensions, the United States should focus its efforts on helping to secure the border with Turkey to stem the flow of foreign fighters into Iraq and getting "help from our [Persian] Gulf allies in the ideological struggle against this perversion of Islam.”

Iraqi forces regained ground from Islamic State militants in western Iraq, advancing toward the city of Ramadi one week after it fell to the insurgents. (Reuters)