Fawaz al-Rabiai told the court in December the men had given a pledge to al-Qaida leader Usama bin Ladin to kill Americans. He had previously been sentenced to 10 years in jail, a verdict that surprised some Yemeni observers. 

The court on Saturday also upheld a death penalty that had been passed in August against one other member of the group. The sentences of two others were raised from 10 to 15 years, while the rest - with jail terms ranging from three to 10 years - stayed the same. 

The Limburg bombing off Yemen's coast in October 2002 killed one of the crew of 25 and ignited a fire on board the supertanker loaded with 400,000 barrels of Saudi Arabian crude oil. 

Other activities

The court sentences included guilty verdicts upheld for other activities, including a plot to kill the US ambassador to Yemen and to attack Western embassies. 

The 2002 Limburg bombing killed
one crew member

It was not clear whether any of the men would turn to Yemen's high court, which has the power to overturn rulings. 

"God is great, there is no god but God and America is the enemy of God," the men shouted after sentencing. 

"(We) were very close to Shaikh Usama bin Ladin. We had given our pledge to Shaikh Usama to kill Americans," al-Rabiai said in his final statement to the court in December, in the clearest admission yet of the group's ties to Bin Ladin. 

Yemen, the ancestral home of Bin Ladin, has cooperated closely with the US-led "war on terror" and has arrested hundreds of al-Qaida suspects since the 11 September 2001 attacks.