The ship was reportedly carrying used military equipment
An investigation has been launched after a US container ship opened fire on a small Egyptian boat as it approached the Suez Canal.
Egyptian sources including the country's official news agency say one man was killed and two injured when the Global Patriot opened fire.
But in a statement the US embassy in Cairo said initial reports indicated there were no casualties.
The US says it simply fired warning shots at the boat.
The US says an investigation into the incident has been launched and it is co-operating fully with the Egyptian authorities.
The US says the Global Patriot - on short-term charter to the US military - was approached by several boats as it prepared to enter the Suez Canal after dark on Monday.
The US statement: "The boats were hailed and warned by a native Arabic speaker using a bullhorn [loudhailer] to warn them to turn away. A warning flare was then fired.
"One small boat continued to approach the ship and received two sets of warning shots 20-30 yards [metres] in front of the bow."
The statement said that all shots "were accounted for as they entered the water", and initial reports from the ship indicated there had been no casualties.
But Egyptian officials and witnesses say a man aboard the boat, Mohammed Fouad, was killed as his boat approached the ship in order to offer goods for sale. Two other men were injured, they say.
This is also the version of events reported by the official Egyptian news agency, citing preliminary reports.
Egyptian sources say Fouad's body was taken to a hospital morgue and then a mosque to await burial on Tuesday.
"We are praying over his body right now," Abbas al-Amrikani, the head of the union of seamen in Suez, told AP news agency, over audible sounds of prayer.
"I saw the body. The bullet entered his heart and went out the other side."
According to the US Navy's Military Sealift Command (MSC), the Global Patriot is a US-flagged roll-on, roll-off container ship chartered from Global Container Lines.
In the past, it has been used by the MSC to transport a US military Patriot Missile defence battery, ammunition, and MRAP (Mine Resistant Ambush Protected) vehicles around the world.
On this occasion, the Global Patriot is said to have been transporting used US military equipment from Dubai.
The BBC's Heba Saleh in Cairo says fisherman and small boats carrying hawkers ply the waters of the canal trying to sell cigarettes and other local products to ship passing through.
Al-Qaeda militants have in the past used small motorboats to attack US military and other foreign vessels in waters off the coast of Yemen, our correspondent adds.
Some 7.5% of world sea trade passes through the Suez Canal, which is 190km long (118 miles) and 300m wide (984ft) at its narrowest point.