RIYADH, Saudi Arabia -- High winds were to blame for the toppling of a massive crane that smashed into Mecca's Grand Mosque and killed at least 107 people ahead of the start of the annual hajj pilgrimage, the head of Saudi Arabia's civil defense directorate said Saturday.
The disaster during a violent thunderstorm that roared through Islam's holiest city late Friday afternoon was the deadliest incident in years surrounding the hajj, which gets underway in full later this month.
Images shared on social media showed a horrifying scene. The crane boom pierced through the roof of the mosque, bringing down slabs of reinforced concrete and leaving bodies lying amid pools of blood on the polished mosque floors as frightened survivors screamed in panic.
The director general of civil defense, Suleiman bin Abdullah al-Amro, told satellite broadcaster Al-Arabiya that the unusually powerful winds that toppled the crane also tore down trees and signs as a storm whipped through the area.
He denied reports that lightning brought down the red-and-white crane, which was being used for the mosque's expansion, or that some of those killed died in a stampede.
"The speed of the wind was not normal," he said. "There was no way for people to know that the crane was about to collapse for them to scramble," he added.
An amateur video circulating online, however, appeared to show a frantic scramble in the moments after the crane collapsed as scores of people pushed and jostled one another in a struggle to get out.
At least 238 people were injured in the accident, according to civil defense figures.
Authorities did not provide details on the victims' nationalities, but it was likely that the tragedy will touch several countries.
U.S. Secretary of State John Kerry expressed his condolences and said the U.S. stands with Saudi Arabia and "all Muslims around the world in the aftermath of this dreadful incident at one of Islam's holiest sites."
The Grand Mosque and the cube-shaped Kaaba within it draw Muslims of all types from around the world throughout the year, though numbers increase significantly in the run-up to the hajj. The mosque is Islam's holiest site, and Muslims the world over pray in the direction of the Kaaba, which is also at the heart of the hajj rituals.
Performing the pilgrimage during one's lifetime is a duty for all able-bodied adult Muslims. This year's pilgrimage is expected to start around Sept. 22.
Nearly 910,000 pilgrims have already arrived in the country for this year's hajj season, according to official figures.
Ahmed bin Mohammed al-Mansouri, the spokesman for the presidency of Mecca and Medina mosque affairs, said in a statement carried by the official Saudi Press Agency that the crane struck a circular area around the Kaaba and a nearby walkway.
The crane was one of several surrounding the mosque to support an ongoing expansion of the sanctuary.
Steep hills and low-rise traditional buildings that once surrounded the mosque have in recent years given way to shopping malls and luxury hotels - among them the world's third-tallest building, a giant clock tower that is the centerpiece of the Abraj al-Bait complex.
The construction giant Saudi Binladin Group is leading the mosque expansion and also built the Abraj al-Bait project.
The Binladin family has been close to the ruling Al Saud family for decades and oversees major building projects around the country. The Binladen family disowned one of its many members, late al-Qaida leader Osama bin Laden, in the 1990s.
During the week of the hajj, Muslims converge on Mecca to perform a series of rituals, including the circling of the Kaaba, praying and holding vigil at Mount Arafat, and the symbolic stoning of the devil by throwing pebbles at the three pillars in Mina.
Prayers on and around the mount are a climactic emotional and spiritual moment in the hajj. The faithful believe that on the day the gates of heaven are open, prayers are answered and past sins are forgiven.
All male pilgrims, regardless of wealth or status, wear seamless terry white cloths to symbolize equality before God during the hajj. Women cover their hair and wear long loose clothing, forgoing makeup and other adornments to help them detach from worldly pleasures and outward appearances.
It was on Mount Arafat, marked by a white pillar, where Islam's Prophet Muhammad is believed to have delivered his last sermon to tens of thousands of followers some 1,400 years ago, calling on Muslims to unite.
While following a route that the prophet once walked, the rites are believed to ultimately trace the footsteps of the prophets Ibrahim and Ismail, or Abraham and Ishmael as they are named in the Bible.
The millions of pilgrims who visit the country's holy sites each year pose a considerable security and logistical challenge for the Saudi government, and large-scale deadly accidents have occurred on a number of occasions in years past.
In 2006, more than 360 pilgrims died in a stampede at the desert plain of Mina, near Mecca. A crush of pilgrims two years earlier left 244 dead.
The worst hajj-related tragedy was in 1990, when 1,426 pilgrims died in a stampede in an overcrowded pedestrian tunnel leading to holy sites in Mecca.