The top U.S. commander in Iraq said Wednesday that "terrorists and death squads" are mainly responsible for a surge in sectarian violence in the capital, and he pledged to provide whatever U.S. forces are needed to avert civil war.

Gen. George Casey, at a joint news conference with U.S. Defense Secretary Donald H. Rumsfeld, told reporters that Al Qaeda is carrying out terrorist killings in the Baghdad area in an attempt to "demonstrate that they are still relevant" after the June 7 killing of their leader in Iraq, Abu Musab al-Zarqawi.

`What we are seeing now as a counter to that is death squads, primarily from Shiite extremist groups that are retaliating against civilians," Casey said. "So you have both sides now attacking civilians, and that is what has caused the recent spike in violence here in Baghdad."

Casey said he was consulting with the Iraqi government on means of counteracting the violence. Asked whether that might include putting more U.S. troops in the Baghdad area, Casey replied, "It may, yes."

"We'll make sure there are adequate forces available for the Iraqis to succeed in Baghdad," he added. Rumsfeld said earlier Wednesday that the number of Iraqi and U.S. troops in Baghdad had recently grown from 40,000 to about 55,000.

Casey and Rumsfeld were meeting later with Prime Minister Nouri al-Malaki and members of his Cabinet, who are under growing pressure to show better results from a monthlong crackdown on violence in the capital.

Rumsfeld said earlier Wednesday on an unannounced visit to an air base north of Baghdad that the new Iraqi government is not yet ready to decide on security issues that will determine the pace of U.S. troop reductions this year.

Speaking to reporters on a flight from Afghanistan, Rumsfeld said the Iraqis are embarked "on a comprehensive review" of their security requirements, as well an effort to reconcile Sunni and Shiite groups to broaden political support for the government.

Asked how long that might take, he said, "I don't talk deadlines."

There now are about 129,000 U.S. troops in Iraq and U.S. officials have expressed hope that the total could be reduced to 100,000 by the end of the year, with further cuts in 2007. Rumsfeld's remarks suggested that the timing and scope of troops cuts is still in doubt.

Rumsfeld was met at his airplane by Casey, who accompanied him to a town hall style meeting with troops at the air base, a major logistics hub for the distribution of supplies to troops throughout Iraq.

In a stuffy auditorium packed with several hundred soldiers, Rumsfeld told the troops he wanted to offer them a definition of "what victory means."

"First and foremost it means helping the Iraqi people take the fight to the enemy," he said. He described the enemy in Iraq as "persistent and ruthless," even after a series of tactical defeats and the loss of Abu Musab al-Zarqawi, the terrorist leader who was killed in a U.S. airstrike in early June.

"These enemies are not going to quit," he said.

Rumsfeld also indicated on his flight to Iraq that he did not expect any change for now in the legal arrangement under which American troops fighting in Iraq are immune from domestic laws. Some Iraqi leaders have questioned that immunity in light of a recent string of allegations of murder and other atrocities committed by U.S. troops against Iraqi civilians.

He said the Iraqis are free to say what they want, but that with regard to the handling of allegations against U.S. service members, "It's being handled as it should be."

He indicated no heightened level of concern about the conduct of U.S. troops and said he did not intend to raise the matter in his talks Wednesday with top commanders, although he did not rule out that they might raise it with him.

Among the most recent cases is the alleged rape and slaying of a young Iraqi woman and the killing of her family members in Mahmoudiyah.

"Ninety-nine percent of the American troops and the coalition forces are performing in a highly professional and a courageous and skillful way," he said. "When allegations like this come up like this obviously it hurts the 99.9 percent of the troops as much as anybody."

In his in-flight remarks to reporters, Rumsfeld emphasized the importance of an Iraqi political reconciliation.

"It's as much a political task as anything," he said. "They're going to have to engage in a reconciliation process" between Sunni and Shiite groups, including the Shiite militias that are engaging in acts of intimidation and violence in the Baghdad area, he said.