A U.S. missile strike killed at least six people Wednesday, hours after the top U.S. military officer told Pakistani officials that America respects Pakistan's sovereignty amid an uproar over American military operations in Pakistan's northwest.

Two Pakistani intelligence officials told The Associated Press that several missiles hit a compound in the South Waziristan tribal region early Wednesday evening. Both officials spoke on condition of anonymity because they are not authorized to speak openly to the media.

The officials said the target was a base for Taliban militants and Hezb-i-Islami, another group fighting U.S. and government troops in neighboring Afghanistan.

They said informants in the area had reported that six people were dead and three more injured. Their identities were not immediately clear, but sources told FOX News that no high-profile targets were killed.

The officials said an unmanned drone of the type used by the CIA and U.S. forces in Afghanistan was heard in the area shortly before the attack.

Maj. Murad Khan, a spokesman for the Pakistan army, said it was looking into the incident.

Earlier Wednesday, the American Embassy said that Adm. Mike Mullen, chairman of the joint chiefs of staff, vowed to respect Pakistan's sovereignty — a commitment apparently aimed at easing controversy over a rash of U.S. attacks on militant havens near the border with Afghanistan.

Mullen met separately with army chief Gen. Ashfaq Parvez Kayani and Prime Minister Yousuf Raza Gilani for what a U.S. Embassy statement called "extremely frank, positive and constructive" discussions.

"The Pakistani leaders reviewed the progress of Pakistan's efforts to combat militancy, violence and terrorism," the embassy statement said. "Adm. Mullen appreciated the positive role that Pakistan is playing in the war on terror and pledged continued U.S. support to Pakistan.

"In this context, Adm. 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," it said.

Mullen arrived the same day that Pakistan's army said its forces have orders to open fire if U.S. troops launch another raid across the Afghan border, raising the stakes in a dispute over how to tackle militant havens in Pakistan's unruly border zone.

Pakistan's government has faced rising popular anger over a Sept. 3 attack by U.S. commandos into South Waziristan, a base for Taliban militants who have been killing increasing numbers of U.S. troops in Afghanistan. Pakistan says about 15 people were killed in the raid, all civilians.

The new firing orders were disclosed by Pakistani army spokesman Maj. Gen. Athar Abbas in an interview Tuesday with The Associated Press.

Abbas said Pakistani field commanders have previously been tolerant about international forces crossing a short way into Pakistan because of the ill-defined and contested nature of the mountainous frontier.

"But after the (Sept. 3) incident, the orders are clear," Abbas said. "In case it happens again in this form, that there is a very significant detection, which is very definite, no ambiguity, across the border, on ground or in the air: open fire."

The statement was the strongest since Kayani raised eyebrows last week by vowing to defend Pakistani territory "at all cost." Abbas would not say whether the orders were discussed in advance with U.S. officials.

U.S. military commanders complain Islamabad has been doing too little to prevent the Taliban and other militant groups from recruiting, training and resupplying in Pakistan's lawless tribal belt.

Pakistan acknowledges the presence of Al Qaeda fugitives and its difficulties in preventing militants from seeping into Afghanistan. However, it insists it is doing what it can and paying a heavy price, pointing to its deployment of more then 100,000 troops in the increasingly restive northwest and a wave of homicide bombings across the country.

The Associated Press contributed to this report.