Lt Gen Pasha has overseen offensives against militants
The military in Pakistan has appointed a new head of the powerful Inter-Services Intelligence (ISI) agency.
Lt Gen Ahmed Shujaa Pasha is a former head of military operations who launched recent offensives against militants near the Afghan border.
He takes over amid mounting US pressure on Pakistan to do more to combat the Taleban and al-Qaeda.
Gen Pasha's appointment is among several changes announced as part of a shake-up in the army's top command.
The BBC's Barbara Plett in Islamabad says the reshuffle will be closely scrutinised by the United States and Afghanistan, which have questioned the ISI's reliability in fighting the "war on terror".
Pakistani observers say the move appears to be an effort by army chief Gen Ashfaq Kayani - who was himself ISI chief until a year ago - to consolidate his control over the military.
Our correspondent says Gen Pasha has been described as a modern professional soldier.
As head of military operations, he was in charge of offensives which troops began last year against pro-Taleban militants in Swat, Waziristan and other areas of north-west Pakistan.
Gen Pasha replaces Lt Gen Nadeem Taj, a loyalist of former President Pervez Musharraf who was appointed less than a year ago.
Observers say it is rare for an ISI chief to spend so short a time in his post.
"These were the changes due over a period of time. This is how the system works in the army," chief military spokesman Maj Gen Athar Abbas told the AFP news agency.
Security analyst and former general Talat Masood told AFP that Gen Kayani had now "completed a team of his choice".
"He will be able to now lead the army with greater confidence."
Gen Kayani has also changed four of nine corps commanders and named a new chief of the general staff.
The ISI has helped kill or capture a number of senior al-Qaeda figures since 2001.
But it has long been accused of collaborating with militants, despite government assurances the agency has been reformed.
The ISI had a key role in funding the Afghan mujahideen and critics say some of its agents still play a double game, viewing certain militant groups as assets to use in Afghanistan and in the dispute with India over Kashmir.
Earlier this year, Pakistan said its intelligence agents had been accused by the US of alerting al-Qaeda-linked militants before the US launched missile attacks against them.
The ISI was also accused of involvement in the bombing of the Indian embassy in Kabul in July. Islamabad denied the allegation.
Gen Pasha's appointment also comes after a major stand-off between the Pakistani government and the army chief, who resisted attempts to put the ISI under civilian control.
But whether his reshuffle will lead to policy changes or reform in the ISI remains to be seen, our correspondent says.
Pakistan's powerful military has ruled the country for about half of its 61 years of independence.
Gen Kayani has indicated he wants to keep the military out of politics but he has shown a tough streak, strongly condemning recent US cross-border raids into north-west Pakistan.