Azerbaijan Airlines initially said the plane flew through a flock of birds before withdrawing the statement.
"We cannot disclose any investigation results at this time," the office of Azerbaijan's prosecutor general said in a statement.
"All possible scenarios are being examined, and the necessary expert analyses are underway," it added.
It said an investigative team led by the deputy prosecutor general of Azerbaijan has been dispatched to Kazakhstan and is working at the crash site.
Survivors 'covered in blood'
A Kazakh woman told the local branch of Radio Free Europe/Radio Liberty (RFE/RL) that she was near where the plane crashed and rushed to the site to help survivors.
"They were covered in blood. They were crying. They were calling for help," said the woman, who gave her name as Elmira.
She said they saved some teenagers.
"I'll never forget their look, full of pain and despair," said Elmira. "A girl pleaded: 'Save my mother, my mother is back there'."
The health ministry said a special flight was being sent from the Kazakh capital Astana with specialist doctors to treat the injured.
Russian President Vladimir Putin held a phone conversation with Aliyev and "expressed his condolences in connection with the crash", his spokesman Dmitry Peskov told a news conference.
A Russian emergency situations ministry had been sent to Aktau with medical personnel and other equipment, Putin said later as he opened the CIS leaders' meeting in Saint Petersburg.
Azerbaijan's first lady Mehriban Aliyeva, who is also the country's first vice president, said she was "deeply saddened by the news of the tragic loss of lives in the plane crash near Aktau".
"I extend my heartfelt condolences to the families and loved ones of the victims. Wishing them strength and patience! I also wish a speedy recovery to the injured," she said on Instagram.
Chechen leader Ramzan Kadyrov said on Telegram: "I express my condolences to the relatives of the passengers of the Azerbaijan Airlines jet who died."