MIAMI, US - A judge handed two brothers prison terms of six and seven years on Wednesday for swearing allegiance to Al-Qaeda and plotting to blow up the Sears Tower, once the tallest building in the world.

US District Judge Joan Lenard found Burson and Rotschild Augustin, who wept as their sentences were read, played a minor role in the 2006 conspiracy and gave them a far lighter sentence than the 30 years prosecutors had sought.

In handing down the sentence against 24-year-old Burson, Lenard said: 'Islamic terrorism is one of the most tremendous problems that this country now confronts... this defendant took an oath to Al-Qaeda.'

But she added that Augustin's actions might have been affected by other factors. 'This was a young man who for whatever reason, perhaps lack of education or lack of direction, came under the influence of Narseal Batiste.'

Augustin's attorney Louis Casuso had asked for leniency, telling the court that 'when you are young, you say a lot of stupid things and you go through a lot of stupid things.'

A US jury in May convicted the group - members of the so-called Liberty Five, named after the Miami neighborhood of Liberty City where they lived - of seeking to contact Al-Qaeda and plot a series of attacks, including blowing up the Sears Tower.

The Chicago landmark has since has been renamed the Willis tower. The five were also convicted of plotting attacks on FBI buildings in the hope of bringing down the US government.

In court filings prosecutors called for Batiste, the group's leader, to be given the maximum penalty of 70 years in prison, 50 years for another member Patrick Abraham, and 30 years for the other three.

At the time it was built in 1973, the 108-story 1,450 feet (442 meter) Sears Tower was the tallest building in the world, surpassing the World Trade Center towers in New York.

It remains the tallest building in the United States and now is the fifth-tallest freestanding building in the world.

Batiste, 35, was convicted on four counts of conspiracy, including providing material support for a foreign terrorist organization, conspiring to provide material support for terrorists, conspiring to blow up buildings with explosives and conspiring to commit seditious acts.

Abraham, 29, was convicted on three counts of conspiracy and faces up to 50 years in prison. The three others were convicted of two counts of conspiracy.

Burson Augustin and his brother Rotschild, 26, were 19 and 20 years old when they joined the group.

Defense lawyers had portrayed the FBI sting operation and ensuing arrests in March 2006 as a play for publicity to highlight the government's campaign against terrorism in the United States.