PORT SAID, Egypt, March 9 (Reuters) - Egyptian protesters in Port Said untied moored speedboats used to supply shipping on the Suez Canal on Saturday, apparently hoping the boats would drift into the waterway and disrupt passing vessels, witnesses said.

About 2,000 protesters also blocked car ferries from crossing the canal, following a court's confirmation of death sentences on 21 local soccer fans.

Military police recovered five of the speedboats and brought them back to shore, but two were still drifting, one witness told Reuters.

Port Said, at the northern entrance to the canal, has suffered frequent eruptions of violence since the death sentences were first handed down on the fans in January for their role in a stadium riot which killed more than 70 people in Port Said last year.

However, until now they had declared the Canal, a major artery for global shipping, off limits for the protests apart from one occasion, when red balloons marked "SOS" were floated into the waterway. The Suez Canal is a major local employer.

In Cairo, other soccer fans set fire to a police social club, with plumes of smoke rising over the capital. (Reporting by Yousri Mohamed; Writing by David Stamp; Editing by Alison Williams)