The ship, Global Patriot, had arrived from the Red Sea and was waiting in the Gulf of Suez to sail to the Mediterranean when a group of Egyptians seeking to sell merchandise approached the boat on small barges, the source said.

Americans on board told the barges to stop and opened fire when they continued to approach.

Several of the small barges that usually ply their trade in small goods on the canal gathered in protest immediately after the shooting but then dispersed, leaving the Suez waterway clear for traffic.

According to the website of the US Navy's Military Sealift Command, the MV Global Patriot is a roll-on roll-off transport ship chartered from Global Container Lines.

An undated photograph of the ship on the company's website shows it without military markings.

The security source said that the ship was expected to cross the Suez Canal as planned at 6:00 am (11am Singapore time) on Tuesday.

The US embassy in Cairo was not immediately available for comment on the incident.

The Suez Canal, which opened in 1869, is Egypt's third-largest source of revenue after tourism and remittances from expatriate workers and currently about 7.5 per cent of global trade passes through the waterway.

It is also a key route for the US military to carry weapons, supplies and troops to and from the Gulf, in particular Kuwait and Iraq. -- AFP