ISLAMABAD, Pakistan - Pakistan's military said Tuesday its ground forces exchanged fire with a NATO helicopter in another flareup possibly involving Washington, but also reported it had arrested a senior al-Qaeda operative.

The two reports highlight some of the complexities of trying to rebuild ties after the U.S. raid that killed Osama bin Laden earlier this month.

Washington needs Pakistan as a partner against al-Qaeda, but Pakistani officials remain deeply angered by the secret operation over their borders in the assault on bin Laden.

In a possible sign of stronger controls at the frontier, Pakistani ground forces traded fire with a NATO helicopter on the Afghan border, and two Pakistani soldiers were wounded, officials said.

The Pakistani army filed a protest, and a NATO spokesman said an "incident" occurred at the border that would be investigated.

Pakistan's army and intelligence agencies have faced uncomfortable international scrutiny since bin Laden was killed inside a compound in the army town of Abbottabad.

U.S. lawmakers have said bin Laden's location was the latest - and strongest - indication that Pakistan protects some terrorists even as it accepts U.S. aid to battle Islamic extremism. Pakistan denies any duplicity.

The army said it had arrested Yemeni national Muhammad Ali Qasim Yaqub - also known as Abu Sohaib Al Makki - who it said was working directly under al-Qaeda leaders along the border.

It did not say when he was arrested but noted he was found in the southern city of Karachi, where several other al-Qaeda leaders have been detained since 2001.

An American official said the suspect was a midlevel al-Qaeda operative and praised the Pakistani military. The official spoke on condition of anonymity to discuss matters of intelligence.

The Pakistani military said Makki's detention was a "major development in unraveling the al-Qaeda network operating in the region."

On Monday, Sen. John Kerry (D., Mass.) met army and civilian leaders in Pakistan during the first visit by an American emissary since bin Laden was killed. With some American lawmakers calling for U.S. aid to Pakistan to be cut, he told them that "action, not words" were needed to tackle extremists.

The NATO firing incident took place in the Datta Khel area of the North Waziristan tribal region, a known sanctuary for Taliban and al-Qaeda extremists who launch attacks inside Afghanistan. It has been targeted repeatedly by U.S. drone strikes.

A similar event last year that killed two Pakistani soldiers prompted the Pakistani army to temporarily close a key border crossing to NATO supplies heading from Pakistan into landlocked Afghanistan, exposing the vulnerability of the war effort.