Riots are once again plaguing Egypt after another raft of death sentences for those involved in last year's Port Said football stadium disaster, which killed 74.

Some 21 men were sentenced to death, and two senior police officers were jailed for 15 years for their handling of the riot.

In Cairo, home to most of the riot's victims, people are angered that 28 other defendants were cleared. There, rioters have torched a police social club and the nearby offices of the Egyptian Soccer Federation.

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Protestors in Port Said- where the defendants come from- have tried, so far unsuccessfully, to disrupt the strategically important Suez Canal.

Witnesses said youths untied moored speedboats which supply shipping on the waterway, hoping the boats would drift into the path of passing vessels. About 2,000 people also blocked car ferries from crossing the canal.

Military police recovered five speedboats and brought them back to shore, but two were still drifting, one witness told Reuters. The army has been in charge of security in central Port Said after police were pulled out on Friday to ease tensions.

Spectators were crushed on 1 February last year after Port Said's local team, al-Masri, beat Cairo's al-Ahly 3-1. Some fell and were crushed, while others were thrown from terraces.

In January, similar riots broke out in Port Said after 21 other men involved in the riot were given death sentences. They left 40 people dead, most of them shot by police.

Among the dead on that day were Abdel-Halim al-Dizawi, a who played for the city's Al-Marikh football team, and Tamer al-Fahla, who used to play for al-Masri.

Unrest has plagued Port Said since those sentences, with locals who want the fans spared fighting pitched battles with police. At least eight people have been killed this week, including three policemen.

Today, Fifa president sepp Blatter tweeted: ""I call on football fans in Egypt to remain peaceful. Violence is never a solution and is contrary to the spirit of sport."