The reported attack adds fuel to the furor in Pakistan over a surge in cross-border operations by U.S. forces putting huge strain on the countries' seven-year antiterror alliance.
Two intelligence officials told The Associated Press that several missiles hit a compound used by Taliban militants and Hezb-i-Islami, another group involved in escalating attacks on U.S. and government troops in neighboring Afghanistan.
They said informants in the area had reported that six people were dead and three more wounded. Their identities were not immediately clear. One of the officials said an unmanned drone of the type used by the CIA and U.S. forces in Afghanistan was heard in the area.
Both officials spoke on condition of anonymity because they are not authorized to speak openly to the media.
Capt. Christian Patterson, a spokesman for the U.S.-led coalition in Afghanistan, said he had no reports of any firing into Pakistan on Wednesday evening. Officials at the U.S. Embassy in Islamabad could not be reached immediately. The White House declined to comment.
Hours earlier in the capital, Islamabad, Adm. Mike Mullen, the chairman of the U.S. joint chiefs of staff, met with Pakistani officials including its prime minister and the chief of the army, both of whom have aired strong protests against cross-border attacks.
According to a U.S. Embassy statement, Mullen "reiterated the U.S. commitment to respect Pakistan's sovereignty and to develop further U.S.-Pakistani cooperation and coordination on these critical issues that challenge the security and well-being of the people of both countries."
U.S. President George W. Bush made a similar statement about Pakistan's sovereignty in July after meeting Pakistani premier Yousuf Raza Gilani in Washington.
Since then, suspected U.S. missile attacks across the Afghan border into Pakistan have intensified, and on Sept. 3, U.S. forces staged a ground assault in South Waziristan, the same region reportedly hit Wednesday.
CBS News National Security correspondent David Martin notes that a fundamental problem that is not going to be solved any time soon is the safe havens in Pakistan.
"The U.S. has stepped up its cross border strikes, mainly using unmanned drones, and that has provoked howls of protest from Pakistan and even threats to open fire on any American troops who cross the border," said Martin.
After the meeting between U.S. and Pakistani military officials, the American embassy in Islamabad put out a statement promising that the U.S. would respect Pakistani sovereignty. What it didn't say -- but which is also true, says Martin -- is the U.S. will continue to protect its troops in Afghanistan and that means going after the sanctuaries in Pakistan.
"In other words, the U.S. respects Pakistani sovereignty but will continue to violate it. Just as the U.S. regrets civilian casualties but can not -- no matter how hard it tries -- avoid them,'' said Martin.
American officials complain Islamabad has not done enough to keep militant groups from using Pakistan's tribal belt as a base from which to plan attacks on U.S. and NATO forces in neighboring Afghanistan. The tribal areas are semiautonomous regions where the Pakistani government has traditionally had limited influence.
"The Pakistani government has to take control on its side of the border and we are working in a variety of ways to help the Pakistani government build its capabilities," Richard Boucher, U.S. Assistant Secretary of State for South and Central Asian Affairs, told reporters in Brussels on Wednesday.
Pakistan insists it is doing its best to flush out militants and paying a heavy price.
It points to its deployment of some 120,000 troops in the northwest, heavy losses suffered by its security forces, ongoing military offensives, and a wave of suicide attacks launched by the Taliban in revenge.
One such offensive, against insurgents in the Bajur border region, has garnered U.S. praise amid signs it is helping reduce violence on the Afghan side of the border. On Wednesday, troops backed by jet fighters killed at least 19 suspected insurgents, officials said. The army says more than 700 suspected militants and 40 troops have been killed in the six-week-old operation. It has declined to give an estimate of civilian casualties.
But the U.S. ground attack and suspected missile strikes have embarrassed Pakistan's government and its powerful military and threaten to fuel simmering anti-American sentiment in the country. Many here complain that Pakistan is being made a scapegoat for Western failures in Afghanistan and that cross-border attacks only fuel militancy.
Army chief Ashfaq Parvez Kayani issued a strong public rebuke to the U.S. last week, insisting Pakistan's territorial integrity "will be defended at all cost" and denying there was any agreement for U.S. forces to operate there.
Maj. Gen. Athar Abbas, the army's chief spokesman, told the AP on Tuesday that Pakistani commanders had received orders to fire on intruding forces following the Sept. 3 attack.
Some analysts said it was unlikely Pakistan would risk the huge sums it receives in American aid by targeting U.S. soldiers or aircraft and its civilian leaders insist that they must solve the issue through diplomacy.
"We cannot pick up guns and say that 'here we are coming,"' Defense Minister Chaudhry Ahmed Mukhtar told Dawn News on Wednesday. "I don't want to say anything which can jeopardize this relationship we have with the Americans on the issue of terrorism."
He said President Asif Ali Zardari would take up the issue on an upcoming trip to Washington.