Libya’s attorney general has been asked by senior politicians to launch an urgent inquiry into the catastrophic floods that have killed tens of thousands of people, including into allegations local officials imposed a curfew on the night Storm Daniel struck.

The Libyan Red Crescent put the death toll at more than 11,000 people, with nearly 20,000 still missing, the highest estimate yet from an official source. It said almost 2,000 bodies were swept into the sea by the floods.

Officials in the port city of Derna including the mayor, Abdulmenam al-Ghaithi, believe 20,000 people may have died. At least 5,500 people have been confirmed dead.

Many have been buried in mass graves but one of the chief shortages in the city, apart from drinking water, is body bags required to prevent disease spreading from unburied bodies. Rescue teams have been able to enter the city and are scouring rubble and ruins left by the floods.

The call for the inquiry came separately from both sides of a country divided between rival eastern and western administrations: Libya’s presidential council chair, Mohamed al-Menfi, in the east, and the interim prime minister of the Tripoli-based government, Abdel Hamid Dabaiba. Menfi said he wanted the inquiry “to hold accountable everyone who made a mistake or neglected by abstaining or taking actions that resulted in the collapse of the city’s dams”.

Libya has been riven between parallel administrations for years, but the attorney general, Al-Siddiq Al-Sour, is one of the few officials left whose writ supposedly runs across the country.

A groundswell of anger is building about whether warnings about the state of the two dams were ignored, the failure to find new contractors to maintain the dam after Libya’s 2011 civil war, and the precise instructions issued by the police and security directorate on the night of the flood.

A Turkish firm, Arsel, had been contracted to work on the dams in 2007 but left Libya in 2011 when fighting broke out and had not returned. Part of a sum of 39m dinars set aside for the dam’s maintenance in 2003 was later taken back from the ministry of water resources. After the company left the country, its machinery was stolen and the building site went into disuse, according to information that was shared with Dabaiba at a meeting with the ministry.

There are allegations officials imposed a curfew on the night the dams collapsed. Photograph: Jamal Alkomaty/AP

Any inquiry would need to examine the circumstances that led to the arrest of the leading candidate to win Derna’s municipal elections, resulting in the elections, scheduled for September, being cancelled and leaving the city under the control of military officials. Derna has been through a variety of different administrations, but the overall area is under the control of the Libyan National Army, led by the authoritarian Gen Khalifa Haftar and his sons.

International aid started to reach the town on Wednesday afternoon, after delays partly caused by disruption of internet access and impassable roads. In all, rescue workers managed to extract 39 people from the rubble on Wednesday, including an entire family. Social media including Facebook were used to broadcast the whereabouts of those needing rescue.

Derna citizens had been very aware of the threat posed by the state of the dams and the Wadi Derna River that runs through the city with no embankment.

Libya: bodies pulled from sea as country reels from deadly flooding – video report

Accusations are being made that officials from the Libyan National Army security directorate may be trying to cover up that as Storm Daniel hit on Sunday night its officials went on TV to instruct citizens to stay in their homes under curfew rather than evacuate.

Wolfram Lacquer, a German-based Libya specialist, said however that it seemed clear that the local police met the mayor on Sunday as the storm approached and that messages were then broadcast from vans across the town calling for an evacuation of areas likely to be affected, but the call may have been met with reluctance.

He said it appeared no maintenance had been carried out on the dam nearest the city since 2011, and money that had been allocated had not been used. Many overseas contractors did not return to Libya after 2011, either because they were pursuing compensation claims or did not regard the country as safe.

“Already, we can see the key political protagonists – the rival governments and Haftar – expend a lot of effort on shaping public perceptions on who is responding and providing assistance. Menfi, for instance, called for the inquiry on the cause of the dam’s collapse to cover any evidence of the obstruction to aid reaching Derna,” Lacquer said.

The core of the two aggregate dams is made of compacted clay, and the sides are made of stones and rocks. Al-Bilad dam, which is about 1km south of the heart of the city, has a storage capacity of about 1.5m cubic metres, while Abu dam, about 13km south of the first dam, has a capacity of about 22.5m cubic metres.

In Derna, the beach was littered with possessions swept out of homes by the torrent that developed at a speed as water poured down from the Green mountains into the river.

The floods have displaced at least 30,000 people in Derna, according to the International Organization for Migration, and damaged or destroyed many access roads to Derna. Local authorities were able to clear some routes, and humanitarian convoys have been able to enter the city.

Rescue teams have arrived in Libya from Egypt, Tunisia, the United Arab Emirates, Turkey and Qatar. Most have now reached the city. Turkey is sending a ship carrying equipment to set up two field hospitals, while Egypt has assembled a near army of rescue vehicles that were paraded in front of the country’s president, Abdel Fattah al-Sisi, before moving across the border.

Patrick Wintour Diplomatic editor