Insurgent commanders "apparently came face to face" with four American officials during meetings on June 3 and June 13 at a villa near Balad, about 25 miles north of Baghdad, The Sunday Times reported.
When asked on NBC's "Meet the Press" about the report of the two meetings, Rumsfeld said: "Oh, I would doubt it. I think there have probably been many more than that."
Under pressure to show progress on Iraq, President Bush appears to be softening his once-firm line against dealing directly with insurgents - now willing to engage something besides military force, CBS News Correspondent Joie Chen reports.
Rumsfeld insisted the talks with insurgents did not involve negotiations with Iraq's most-wanted terrorist, Jordanian-born Abu Musab al-Zarqawi, but were rather facilitating efforts by the Shiite-led government to reach out to minority Sunni Arabs, who are believed to be the driving force behind the insurgency.
In other developments:
The first attack happened when a suicide bomber with explosives hidden beneath watermelons in a pickup truck slammed into a two-story police station near a market at a police headquarters, killing 10 policemen and two civilians and wounding eight more, U.S. Army Capt. Mark Walter said.
Less than two hours later, a suicide bomber blew himself up in a parking lot outside an Iraqi army base, killing 16 and wounding seven more, Walter said. Almost all of the victims were civilian workers arriving at the site, he said.
A third attacker strapped with a belt of explosives walked into Mosul Jumhouri Teaching Hospital and blew himself up in a room for police officers guarding the facility, killing five policemen and wounding 12 others, police Brig. Gen. Wathiq Mohammed Tahr said.
Mosul, the country's third-largest city, is 225 miles northwest of Baghdad and considered an insurgent stronghold. Abu Musab al-Zarqawi's al Qaeda in Iraq claimed responsibility for the attacks. The claim, made on an Internet site used by militants, could not be verified.
Meanwhile, Rumsfeld downplayed the significance of the Sunday Times' report on the meetings with insurgents.
"We see the government of Iraq is sovereign. They're the ones that are reaching out to the people who are not supporting the government," Rumsfeld said on "Meet the Press."
"They're not going to try to bring in the people with blood on their hands, for sure, but they're certainly reaching out continuously, and we help to facilitate those from time to time."
The Sunday Times report, which quoted unidentified Iraqis whose groups were purportedly involved in the meetings, said the insurgents at the first meeting included the Ansar al-Sunnah Army, which claimed responsibility for suicide bombings in Iraq and a Christmas attack that killed 22 people in the dining hall of a U.S. base at Mosul.
The group rejected the report, denying in an Internet statement meeting with any "crusader or renegade," and that jihad, "holy war," was the only way to retrieve the "grace and dignity" of the Muslim nation.
Two others named were Mohammed's Army and the Islamic Army in Iraq, which in August reportedly killed Italian journalist Enzo Baldoni, the newspaper said.
One American at the talks introduced himself as a Pentagon representative and declared himself ready to "find ways of stopping the bloodshed on both sides and to listen to demands and grievances," The Sunday Times said.
The official indicated that the results of the talks would be relayed to his superiors in Washington, the newspaper said.
Rumsfeld did not provide details about any meetings, saying the insurgency had many layers, ranging from disaffected Sunni members of Saddam Hussein's ousted regime to foreign-born terrorists.
"There's no one negotiating with Zarqawi or the people that are out chopping people's heads off," he said.
"I would not make a big deal out of it. Meetings go on frequently with people," Rumsfeld told Fox News Channel.
The U.S. officials tried to gather information about the structure, leadership and operations of the insurgent groups, which irritated some members, who had been told the talks would consider their main demand, a timetable for the withdrawal of U.S. forces from Iraq, the newspaper said.
During the June 13 talks, the U.S. officials demanded that two other insurgent groups, the 1920 Revolution and the Majhadeen Shoura Council, cut ties with al-Zarqawi's group, al Qaeda in Iraq, according to the report.
A senior U.S. official said earlier this month that American authorities have negotiated with key Sunni leaders, who are in turn talking with insurgents and trying to persuade them to lay down their arms. The official, who did not give his name so as not to undercut the new government's authority, did not name the Sunni leaders engaged in dialogue.