He fled to Pakistan following the deposition of the Taliban in late 2001, and was reported to have rallied 1,000 fighters by March 2002. Saifullah was reported to have said "The fight against America for the supremacy of Islam and the defense of our country will continue until our last breath".
In May 2002 Time magazine described Saifullah as an emerging hero in the Taliban, after his men destroyed an American helicopter, killing seven American soldiers. Saifullah was reported by Pahjwok Afghan News to have said "The fight against America for the supremacy of Islam and the defense of our country will continue until our last breath".
In 2005 Pakistani officials offered contradictory comments about whether Saifullah was still alive.
- "Battle Creates a New Taliban Legend". Time magazine. 2002-05-07. "Nobody's seen Mullah Omar lately, but the Taliban and their supporters have a new icon. Saifur Rahman Mansoor, the youthful commander of the Shahi Kot fortress, has emerged as something of a celebrity among anti-American elements in Afghanistan since his men downed a U.S. helicopter and killed seven American soldiers Monday."
- Hamim Jalalzai (2008-01-12). "Dreaded Taliban commander killed in Parachinar". Pahjwok News. "A source in the National Intelligence Department's press office confided to Pajhwok Afghan News that Maulvi Saifur Rehman Mansoor - dreaded Taliban commander for Khost and Paktia provinces - was eliminated along with Sirajuddin in the Pakistani town that was hit by deadly sectarian violence earlier in the month."
- Muḥammad ʻĀmir Rānā, Rohan Gunaratna (2007). Al-Qaeda fights back inside Pakistani Tribal Areas. Pak Institute for Peace Studies. "the leading character in this confrontation, is Saif ur- Rehman, the son of Jihadi commander Nasrullah Mansoor."
- OARDEC (20050-12-20). "Unclassified Summary of Evidence for Administrative Review Board in the case of Shayed, Mohammed Ali Shah". United States Department of Defense. pp. pages 87–89. Retrieved 2008-05-25.
- Terry Bryant (2007). History's Greatest War. Global Media. ISBN 978-81-89940-63-8. "A Taliban fugitive in Paktia province, Mullah Saifur Rehman, also began reconstituting some of his militia forces in support of the anti-U.S. fighters. They totalled over 1,000 by the beginning of March 2002."
- "Taliban commander: Prepared to die for Islam". IPR Strategic Business Information Database. 2002-03-06. Retrieved 2010-12-11. "The private Afghan Islamic Press (AIP) quoted a statement from Commander Maulvi Saif-ur-Rehman Mansoor as saying the jihad, or holy war, against the United States would continue [...] "The fight against America for the supremacy of Islam and the defense of our country will continue until our last breath," stated Mansoor's statement, read to AIP by a spokesman via satellite telephone from the Arma mountains, about …"
- "Conflicting statements on Taliban commander's fate". Pajhwok Afghan News. 2005-04-28. "Senior officials of the southern Paktika province on Thursday came out with contradictory statements on the fate of Taliban commander Saifur Rehman Mansoor, known for spearheading a tough resistance to US forces in Shahikot mountains."
- "Arrested militant reveals 26/11 attackers were trained in Pakistan". India Vision. 2010-11-26. Retrieved 2010-12-10. "‘For Nawab Shah, Abu Hamad was the ‘Masool, Faisal Nadeem was the zonal ‘Masool’ and Saifullah Mansur was the state ‘Masool’."