A billboard of the Syrian president that once overlooked a central square in Aleppo has been burned almost beyond recognition, but the influence of Bashar al-Assad is still felt in the now rebel-held city as residents live in fear of bombardment by his regime.

“The biggest fear, one shared by all the people of Aleppo right now, is the airstrikes,” said Mahmoud, a 50-year-old man who declined to share his family name, concerned that Assad could regain control of the city and punish accused critics as he did eight years ago.

Damascus, backed by the Russian military, has pummelled neighbourhoods across central Aleppo and neighbouring Idlib with airstrikes since insurgents seized control of Syria’s second city last weekend while army forces retreated south.

Two days ago, Mahmoud heard a strike hit in his neighbourhood close to the entrance of Aleppo university hospital. The next day, a wave of airstrikes struck five healthcare facilities in Idlib and a camp for the displaced, killing at least 18 people, and more strikes targeted central Aleppo. On Tuesday afternoon, a strike hit a rural area to the city’s south-east, injuring four.

Mahmoud said he was now avoiding filling up his car at any of the few petrol stations in Aleppo that still have fuel, fearing that the long lines of cars could be a target. “We’ve seen this before,” he said. “We know this regime doesn’t care about people’s lives.”

For the residents of Aleppo, the main sign that Islamist militants from the group Hayat Tahrir al-Sham (HTS) are now in control of the city are the pickup trucks full of armed fighters on the streets, or the militants in their green camouflage uniforms standing on street corners.

Insurgents in civilian clothes guard shuttered government buildings, banks remain closed and many of the estimated 2 million residents of Aleppo have opted to remain home. The UN’s office for humanitarian affairs (OCHA) describes “long queues for bread under precarious conditions”.

Electricity has flickered back on for several hours after long cuts in recent days, but water and power remain intermittent. Although Damascus promised to retain telecoms services in the city, the two main Syrian mobile networks remain out of service. Residents depend on their home internet services to keep in touch with their neighbours over social media.

“I heard HTS and other groups are trying to reinstate the internet, but they’re just starting in one area and they might need time to expand as Aleppo is so big,” said Mahmoud. “I think it’s just a matter of time before more services are provided.”

He disliked seeing the fighters in pickup trucks patrolling the streets, but said he was yet to interact with them. Mahmoud felt reassured about the intentions of HTS – and its nominal political arm, the Salvation government, in Idlib – for governing Aleppo after he attended a speech given by an imam at a mosque in the central al-Mohafaza neighbourhood.

Standing in front of its bright blue tiles and polished stone archways, imam introduced himself as a returning preacher with long-held ties to the neighbourhood.

“None of you will be harmed, not your money, not your religion, not your honour,” said the imam, adding that representatives from the Salvation government would ensure basic services and keep the city’s bread ovens on.

“God forbid if anyone has been subjected to abuse, don’t keep silent … we will not allow any of you to be harmed,” he told them.

Despite their promises to keep the lights on and bread ovens warm, along with pledges of protection, the insurgents remain unable to shield those in newly opposition-held areas from airstrikes.

Mohammed al-Bashir, the nominal prime minister appointed by the Salvation government, condemned the strikes launched by Damascus as “brutal crimes”.

The humanitarian coordination office for north-west Syria, a body that normally attempts to regulate aid into rebel-held Idlib, appealed to the UN and its security council to act and protect civilians from the waves of airstrikes launched by Damascus and their Russian allies.

Syrian civil defence, known as the White Helmets, said that as of 1 December, Syrian and Russian airstrikes on Aleppo and Idlib had killed 56 people and wounded 238 since HTS launched its sweeping operation last week.

Mustafa Abedou, a pharmacist and medic, said he was among crowds of people who fled Idlib for a refugee camp on its outskirts, fearing the centre of the opposition-held city would be targeted.

Instead, he said, the camp was targeted along with Idlib’s residential neighbourhoods yesterday in a wave of airstrikes targeting locations far beyond the frontlines. Abedou said he feared he could hear another jet in the sky as he spoke.

“The Assad regime attacks any city that is no longer under their control, like Aleppo,” he said. “These war planes are attacking vital sites, hospitals or markets to press on opposition forces. It’s terrible, and everyone is afraid of these attacks, even though the battle is almost 20 miles away.”

Syria’s state news agency said Syrian and Russian warplanes launched more air and missile strikes into southern Idlib on Tuesday. Areas of northern Hama, where insurgents fought to claim towns north of the provincial capital, were also said to have been attacked.

Assad’s willingness to employ massive force against his own population reminded Abedou and Mahmoud of battles from the height of Syria’s bloody civil war, including Damascus’ fight to take control of Aleppo that ended in 2016.

Abedou, who also works for the medical relief organisation MedGlobal, said an ambulance driver from their team and a security guard were killed in the strike on Aleppo university hospital earlier this week.

He said he feared Assad’s willingness to resume the airstrikes that brought the city to its knees a decade ago. Doctors across Idlib and Aleppo, he added, had begun circulating training materials about how to respond should Assad choose to employ chlorine gas attacks as he did in the past, or even the deadly nerve agent sarin which his regime used to kill more than 1,400 people in a Damascus suburb in 2013.

“We are afraid, maybe he will use these things again. There are no red lines for this regime, and he might attack again,” said Abedou.

Mahmoud said he and others also fear the airstrikes, but he is growing increasingly concerned about supplies of food and basic medicines. Food prices for many essentials such as tomatoes, peppers and sugar have doubled. The Syrian pound had fallen in value on Aleppo’s hidden market since the insurgent takeover, making goods even more expensive.

“I fear it’s only a matter of time before things become more chaotic, maybe with people taking the opportunity for looting, and that food and medicine could become scarce. Some pharmacies are open, but if they can’t bring new supplies they will run out,” he said.

“People aren’t working which means they aren’t getting paid, especially people working with the state or government, so they won’t be able to buy basic food and necessities.”

“Uncertainty is what rules for all the people in Aleppo, it’s very hard to anticipate what might happen next,” he said. “Including whether the regime will launch an all-out attack to recapture the city.”

Ranim Ahmed contributed reporting