WASHINGTON — Al Qaeda is consolidating its leadership in the territory under its control in Pakistan.

Osama bin Laden’s son and heir apparent, Sa’ad bin Laden, has returned to Pakistan from his safe haven in Iran, according to messages posted on a Qaeda jihad Web forum known as al-Hesbah.

An organization that tracks and translates discussions on such forums, the SITE Institute, provided its subscribers with a summary of messages describing what it said was an escape by Sa’ad bin Laden from an Iranian prison. American counterterrorism officials, however, have considered him to be under a permissive version of house arrest since the American invasion of Afghanistan, in 2001.

The move of Sa’ad bin Laden to Pakistan tracks with the movements of other senior jihadists to the country since Al Qaeda re-established a safe haven in the 10,500-square-mile area that comprises the provinces along the border with Afghanistan.

It also could signal a new phase of Iran’s relationship with Al Qaeda. For the last year, public messages from the terrorist organization’s second in command, Ayman al-Zawahri, have accused Iran of collaborating with America in fighting Al Qaeda in Iraq. Leaders of the Iraqi tribal uprising against Al Qaeda, however, have said Iran has collaborated with their foes.

While Al Qaeda, a Sunni Salafist organization, regards the Shiite theocracy of Iran as an apostate form of Islam, the two sides in the past have worked together through Iran’s Quds Force, an elite unit of the Iranian army. In 2001, following the American invasion of Afghanistan, most of Al Qaeda’s leadership fled to Pakistan. But others, including Sa’ad bin Laden and Saif al-Adel, fled to eastern Iran.

In 2003, before and after the initial invasion of Iraq, Iranian and American negotiators in Geneva discussed a possible swap of the senior Al Qaeda leaders in Iran for members of an Iranian opposition group, the People’s Mujahedin, who were captured in Iraq.

The American government considers the People’s Mujahedin, or MEK, a foreign terrorist organization because of attacks it has carried out inside Iran. Nonetheless, the organization was the first publicly to disclose the existence of the Natanz nuclear facility in 2002, kick-starting the current nuclear standoff between Iran and the international community.

Negotiations over a MEK-Qaeda prisoner swap broke off after American intelligence agencies intercepted a message from Mr. Adel, a senior Qaeda member indicted for taking part in the 1998 bombings of two American embassies in Africa, to the plotters of the May 2003 terrorist attacks in Riyadh, Saudi Arabia.

An American counterterrorism official told The New York Sun that America and allied intelligence services had been aware of negotiations to return senior Qaeda leaders to the group’s safe haven in Pakistan from Iran for nearly a year. But the recent messages on al-Hesbah provided the final confirmation that Sa’ad bin Laden has returned to Pakistan.

The SITE Institute translation of an exchange on the forum between “Asad al-Jihad 2” and “al-Gharib al-Ha’ili” suggests that the news was meant to be hidden at first from even fellow believers.

“Asad al-Jihad 2” writes: “Dear brother, we know a lot of matters, including what concerns Sa’ad, the son of Sheikh Osama, but we do not write. Did the brothers permit you to post them?!! Or is it just an effort on your part?!!”

“Al-Gharib al-Ha’ili” responds: “Brother, Asad al-Jihad 2, it is not an effort. I only wrote what I was permitted to post without any details.”

In the next post, “al-Gharib al-Ha’ili” writes that his initial message about Sa’ad bin Laden was mistaken, but another jihadist later posted that the original information was correct. The messages contain a mention of at least four Al Qaeda leaders who have returned from Iran.

The intelligence community has suspected since June, according to ABC News, that Sa’ad bin Laden has returned to Pakistan to be with his father, who is believed to be hiding out along the Afghan-Pakistani border.

A counterterrorism official told the Sun that hosting Sa’ad bin Laden was “an insurance policy for Iran,” which the official said gave Iran leverage with Al Qaeda because the state was responsible for the well-being of the leader’s son.