An Oregon man pleaded guilty on Friday to being an accessory after the fact for helping people linked to a suicide bomb attack on the headquarters of Pakistan's intelligence service in 2009 that killed about 30 people, court records showed.

Reaz Qadir Khan, a naturalised US citizen living in Portland, admitted in a plea entered in US District Court that he provided advice and financial aid to the suicide bomber's Maldives-based wives following the attack, knowing that such assistance would hinder and prevent their capture.

Khan, a 51-year-old wastewater treatment plant operator and married father-of-three originally from Pakistan, was arrested in 2013 on an indictment which accused him of using email and intermediaries to consult with and provide financial support to the Maldivian bomber, Ali Jaleel, and his family.

The indictment said the conspiracy began in 2005 and continued on through the May 27, 2009, attack on Pakistan's Inter-Services Intelligence headquarters in Lahore and into the following month. The attack also wounded some 300 people.

The government said at the time that the attack, believed to have been carried out by Jaleel and two other people, was in apparent revenge for an army offensive against Taliban militants in the country's northwestern Swat region.

US prosecutors said a video released by the media wing of Al Qaeda soon afterward showed Jaleel taking responsibility for the attack, as well preparing for the assault at a training camp believed to be in the Federally Administered Tribal Areas of Pakistan.

The US Department of Justice said in a statement that under the plea agreement, the defence and government were jointly recommending a prison term of 87 months for Khan. His sentencing is scheduled for June 8.