An EgyptAir official says more wreckage of the missing flight MS804 has been found, including human remains, luggage and passengers' seats, the Associated Press news agency has reported.

"The Egyptian navy was able to retrieve more debris from the plane, some of the passengers' belongings, human remains, and plane seats," the Civil Aviation Ministry said in a statement on Friday.

An unnamed official from EgyptAir said the search was continuing to locate the rest of the plane and the "black box" flight recorders to determine what exactly happened.

Earlier in the day, the Egyptian army said that wreckage was found 290km north of the port city Alexandria on the Mediterranean coast.

The plane disappeared over the Mediterranean with 66 people on board early on Thursday.

EgyptAir Chairman Safwat Moslem told state television that the current radius of the search zone was 65km, giving an area of 12950 sq km but that it would be expanded as necessary.

Egyptian Prime Minister Sherif Ismail said it was too early to rule out any cause for the crash.

READ MORE: Families wait for answers after EgyptAir flight goes missing

Egyptian President Abdel Fattah el-Sisi expressed his condolences on Friday to the families of victims.

"The presidency with utmost sadness and regret mourns the victims aboard the EgyptAir flight who were killed after the plane crashed in the Mediterranean on its way back to Cairo from Paris," Sisi's office said in a statement.

The search intensified on Friday, a day after Egypt's aviation minister said while it was too soon to say why the Airbus A320 flying from Paris to Cairo had vanished from radar screens, a "terrorist" attack would be a more likely scenario than a technical failure.

The tragedy raised fears of a repeat of the bombing of a Russian passenger jet by the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group over Egypt last October that killed 224 people.

The plane disappeared between the Greek islands and the Egyptian coast without a distress signal from its crew.

Kammenos said the aircraft swerved sharply twice in Egyptian air space before plunging 6,700 metres.

Aviation analyst Tobias Rueckerl told Al Jazeera it was likely the searchers would find the black box quickly after locating the crash site, which could shed more light on what happened to the ill-fated aircraft.

"Basically we will have all the details up to the fatal event," Rueckerl said. "If anything happened in the cockpit, it is likely they will hear it on the voice recorder. We don't know the cause of the crash right now."

Both Egypt and Greece dispatched aircraft and naval vessels. They were expected to be joined by French teams, while the US sent a surveillance plane to help with the operation.

READ MORE: Search stepped up for missing EgyptAir flight

Richard Marquise, a former FBI agent who led the US task force investigating the Lockerbie bombing, told Al Jazeera that Egypt was quick to point to an attack, unlike France.

"It's becoming a game of finger-pointing about who's responsible, whether it's a mechanical failure of EgyptAir, or a terrorist bomb on the aircraft," he told Al Jazeera.

He added this was in contrast to the October 2015 Metrojet bombing, when Egypt was more reluctant than Russia to point to a possible attack. In that case, Egyptian authorities were responsible for security as the city of Sharm el Sheikh was the departure point.

Officials from a number of US agencies told Reuters news agency that reviews of satellite imagery so far had not produced any signs of an explosion. They said the United States had not ruled out any possible causes of the crash, including mechanical failure, terrorism, or a deliberate act by the pilot or crew.