A Kenyan man was convicted Monday of plotting a 9/11-style attack on a US building on behalf of the terrorist organisation al-Shabab.

A federal jury in Manhattan found Cholo Abdi Abdullah guilty on all six counts he faced for conspiring to hijack an aircraft and slam it into a building, according to court records.

He's due to be sentenced next March and faces a mandatory minimum of 20 years in prison.

Abdullah represented himself during the trial, which opened last week. He declined to give an opening statement and did not actively participate in questioning witnesses.

In court papers filed ahead of the trial, prosecutors said Abdullah intended to "merely sit passively during the trial, not oppose the prosecution and whatever the outcome, he would accept the outcome because he does not believe that this is a legitimate system.”

Lawyers appointed to assist Abdullah in his self-defence didn't respond to an email seeking comment Monday.

Federal prosecutors, who rested their case Thursday, said Abdullah plotted the attack for four years, undergoing extensive training in explosives and how to operate in secret and avoid detection.

He then moved to the Philippines in 2017 where he began training as a commercial pilot.

Abdullah was almost finished with his two-year pilot training when he was arrested in 2019 on local charges.

He was transferred the following year to US law enforcement authorities, who charged him with terrorism related crimes.

Prosecutors said Abdullah also researched how to breach a cockpit door and information “about the tallest building in a major US city” before he was caught.

The State Department in 2008 designated al-Shabab, which means “the youth” in Arabic, as a foreign terrorist organisation. The militant group is an al-Qaida affiliate that has fought to establish an Islamic state in Somalia based on Shariah law.