- Mexico City metro collapse
media captionEmergency crews attended the collapse near the Olivos station on the metro's 12 Line
A preliminary report into the deadly collapse of a metro overpass in Mexico City last month has found that it was caused by flaws in the construction.
Jesús Esteva, head of the city's public works department, said deficiencies had been found in building materials and structural supports along the line.
More reports will be made in the coming months about the collapse, which happened on 3 May.
The incident killed 26 people and has led to protests in the Mexican capital.
It has also put pressure on allies of President Andrés Manuel López Obrador, and on Mexican billionaire Carlos Slim, Latin America's richest man, whose construction firm Grupo Carso was involved in building the section of train line that collapsed.
The crash happened at around 22:00 local time near Olivos station on the metro's Line 12, in the south-east of the city.
In its probe, Norwegian auditor DNV, found six deficiencies in its construction.
image copyrightReutersimage captionThe incident happened late at night
These included missing bolts on some girders, and unfinished or poorly executed welding.
Experts also found deformations and fractures in support beams of the section that collapsed.
Two further phases of DNV's report will be released in July and August.
Mexico City Mayor Claudia Sheinbaum said that a special team will be created to repair and reinforce the metro line.
She has faced criticism about the line's maintenance. A local labour union said its earlier warning about damage had been ignored by city authorities.
image copyrightGetty and Google Mapsimage captionImages show the site of the incident now and in 2019
Under the spotlight is also Foreign Minister Marcelo Ebrard, who directed the route's construction in 2012 when he was the city's mayor.
Both of them are allies of President López Obrador, and are seen as potential contenders for the presidency when his term ends in 2024.
In a statement, Mr Ebrard, defended how his mayoral administration had overseen construction of the line. He added that a broader enquiry should be made into the decision-making processes of its design, supervision and maintenance.
Line 12, known as the Golden Line, was built at a cost of around $1.2bn (£860m) – about 70% more than was originally planned.
Operations were suspended at a dozen stations along the line in 2014, for over a year, due to deteriorating conditions along the track.
Before the latest report was published, President López Obrador said those responsible for its collapse would be punished.
Prosecutors are investigating the disaster but have yet to publish their findings.