Adm Mullen wants new tactics to help beat the Taleban
America's top military commander, Adm Michael Mullen, has met Pakistani officials to discuss operations along the troubled border with Afghanistan.
Adm Mullen met Prime Minister Yousuf Raza Gilani "to defuse tension", the state news agency APP said. Army chief Gen Ashfaq Kayani was also present.
The visit comes after Pakistan's army said it would not tolerate incursions.
Tension has been rising in Pakistan over an increase in US attacks along the border with Afghanistan.
Adm Mullen arrived on his unannounced visit to Islamabad on Tuesday evening and met Prime Minister Gilani on Wednesday.
The men discussed "measures to defuse tension between the two countries, following a spate of air and ground violations along the Pakistan-Afghan border", APP said.
The US embassy in Islamabad said: "Admiral Mullen reiterated the US commitment to respect Pakistan's sovereignty and to develop further US-Pakistani co-operation and co-ordination on these critical issues that challenge the security and well-being of the people of both countries."
Earlier this month, Adm Mullen said he was not convinced Western forces were winning in Afghanistan.
He called for "a new, more comprehensive strategy" to deny militants bases across the border in Pakistan.
His visit come two days after Pakistani troops were reported to have fired shots into the air to stop US troops crossing into the South Waziristan tribal area.
The tribal region is one of the main areas from which Islamist militants launch attacks into Afghanistan.
Pakistan's military confirmed firing but denied that Pakistani troops were involved.
Army spokesman Major General Athar Abbas told the Associated Press on Tuesday that "no incursion is to be tolerated".
But he stressed to the BBC that no specific orders had been given to open fire if US troops crossed the border from Afghanistan.
Meanwhile, British Justice Secretary Jack Straw, who is also in Islamabad, says operations along the border should be done "in a way that is not counterproductive".
"We believe that these matters have to be subject to consent of the Pakistan government because Pakistan is a sovereign nation," he told the BBC on Tuesday.
It emerged last week that US President George W Bush has in recent months authorised military raids against militants inside Pakistan without prior approval from Islamabad.
Pakistan's army fired shots to deter US troops, reports say
The BBC's Barbara Plett in Islamabad says there is a growing American conviction that Pakistan is either unwilling or unable to eliminate militant sanctuaries in its border area.
There have been a number of missile attacks aimed at militants in Pakistan territory in recent weeks.
Pakistan reacted with diplomatic fury when US helicopters landed troops in South Waziristan on 3 September. It was the first ground assault by US troops in Pakistan.
Locals in the Musa Nikeh area said American soldiers attacked a target with gunfire and bombs, and said women and children were among some 20 civilians who died in the attack.
Pakistan's army has warned that the aggressive US policy will widen the insurgency by uniting the tribesmen with the Taleban.