Cairo(CNN) A Russian passenger plane crashed early Saturday in Egypt's Sinai Peninsula, killing all 224 people aboard, officials said.
Russian state media reported that many of the 217 passengers on Kogalymavia Flight 9268 were Russians returning from vacation. The passenger manifest included 17 children but Russian officials said there were 25 aboard. There were seven crew members.
Ukrainian Foreign Minister Pavlo Klimkin tweeted that four victims were Ukrainian nationals.
The cause of the crash still is unknown, but it is most likely due to a technical failure, and there is no evidence of any terrorist action, Egyptian Airports Co. chief Adel Al-Mahjoob told CNN Arabic.
The Airbus A321 had a routine check before flight, showing everything was OK to proceed, Mahjoob said.
The so-called black boxes -- the flight data recorder and voice data recorder -- have been recovered and transported to Cairo for analysis, Egyptian Civil Aviation Minister Hossam Kamel said at a news conference.
"There was nothing abnormal before the plane crash," he said. "It suddenly disappeared from the radar."
Air traffic control recordings did not show any distress calls, Kamel said.
The plane departed the Red Sea resort of Sharm el-Sheikh, near the southern tip of the Sinai, on a flight to St. Petersburg, Russia. It vanished from radar 23 minutes into the flight, at 6:20 a.m. local time.
Egypt has been battling insurgents in the Sinai aligned with the terrorist group ISIS.
Islamists militants in the Sinai linked to ISIS claimed responsibility for the crash, according to an online statement.
But Russian Transport Minister Maxim Sokolov said the claim that terrorists brought down the plane by using an anti-aircraft missile "cannot be considered reliable," according to Russian state news agency RIA Novosti.
German air carrier Lufthansa and Air France have decided to reroute aircraft due to fly over the region.
"We will keep that measure in place as long as we are not sure of the circumstances and the reasons of the Metrojet crash," Lufthansa spokeswoman Bettina Rittberger said.
At 2 a.m. Sunday, Russians were still going by Pulkovo Airport in St. Petersburg, dropping off red or white carnations and stuffed toys for children. A table held a dozen candles.
Many of the mourners silently paused in front of the memorial before leaving.
Inside the airport, psychologists were available for family members. Some of the relatives were waiting for the bodies of their loved ones to be returned.
Officials said that would begin later Sunday. About 115 people had given DNA samples to help identify the dead.
Among the significant, if preliminary, pieces of information to emerge Saturday were these:
• The plane was flying above 30,000 feet when it disappeared from radar screens, the Egyptian civil aviation ministry said.
• Russia 24, a state-owned news channel, and other Russian media outlets are saying the pilot reported technical problems and requested a landing at the nearest airport before the plane went missing. Officials have not corroborated those reports.
• Russia 24 also quotes the FlightRadar 24 website as saying the plane was descending at a rate of 1,800 meters per minute, or 67 mph, before radar contact was lost.
• Weather in the area was clear, CNN reported.
• The plane was Kogalymavia Flight 9268. The airline is commonly known as Metrojet.
• The crash site is in the northern part of Sinai, near a town called Housna -- 300 kilometers (185 miles) from Sharm el-Sheikh, the Egyptian Prime Minister's office said.
• The site is reported to be in a mountainous area. Still, Egyptian rescue crews made their way there, and officials said 129 bodies have been found and are being flown to Cairo. Ambulances have so far moved 34 bodies to the official Zeinhom morgue and other hospitals in the Egyptian capital.
Analysis: Plane crashed at what should have been flight's safest point
Egyptian Prime Minister Sherif Ismail met with ministers and security officials as the cause of the crash remained a mystery. The most dangerous parts of any flight are the takeoff and landing; it is unusual for a plane to fall from the sky at cruising altitude.
Russian President Vladimir Putin ordered Prime Minister Dmitry Medvedev to open an investigation into the crash, the Kremlin said. And Putin declared an official day of mourning Sunday for the victims.
Egyptian President Abdel Fattah el-Sisi called Putin to express his condolences, according to the Kremlin.
Sisi "assured Mr. Putin that conditions will be created for the broadest possible participation of Russian experts in the investigation of the plane crash," the Kremlin statement said.
U.S. Secretary of State John Kerry spoke to Russian Foreign Minister Sergey Lavrov to express his condolences and offer American assistance if needed, according to the State Department.
The Russian emergency ministry said it was sending five planes to the area to help with possible rescues and the investigation. And Russia opened a hotline for relatives, many of whom gathered at the airport in St. Petersburg, where they had expected their loved ones to arrive.
About 115 relatives have given DNA samples to help identify the victims.
At a St. Petersburg airport terminal, a makeshift shrine was set up for those who perished, with roses, candles and stuffed animals.
Airbus, the plane's maker, issued a statement on Twitter: "We are aware of the media reports," the tweet reads. "Efforts are now going towards assessing the situation. We'll provide more information as soon as available."