A powerful Syrian rebel group has been accused of taking advantage of an internationally brokered ceasefire in the north of the country to carry out a wave of arrests against civilians.

Hayat Tahrir al-Sham, an extremist group that controls roughly two-thirds of Idlib province and counts former al-Qaeda-linked fighters in its ranks, has arrested 184 people since the beginning of September, according to a war monitor.

Among those targeted were activists who had criticised the group, as well as preachers and aid workers, said the UK-based Syrian Observatory for Human Rights. The observatory, which relies on a network of sources inside Syria, said the group had also killed five civilians in raids and by opening fire on demonstrations against it.

“We recorded a significant escalation of Hayat Tahrir al-Sham violations in north Syria, where the group has raided a number of villages and arrested dozens of individuals, including local activists, relief workers and mosque preachers,” the observatory said in a 10-page report.

The crackdown began just two weeks before Russia and Turkey reached a ceasefire agreement that was widely credited with preventing a devastating Syrian government offensive against the last opposition-held part of Syria. Turkey, which backs a number of rebel groups in Idlib, engaged in weeks of intensive diplomacy to prevent the long-threatened assault, fearing it would send another wave of refugees to its border.

As part of the deal, Ankara committed to jointly patrol a buffer zone with Russia – an ally of President Bashar al-Assad – that would be free from heavy weapons and extremist fighters. The agreement has largely been implemented, but Hayat Tahrir al-Sham has sent conflicting messages about whether it would fully comply.

“We value the efforts of all those striving – at home and abroad – to protect the liberated area and prevent its invasion and the perpetration of massacres in it,” the group said in its first public statement on the deal last week.

Syrian families waiting in the shadows of Lebanon's refugee camps Show all 20 1 /20 Syrian families waiting in the shadows of Lebanon's refugee camps Syrian families waiting in the shadows of Lebanon's refugee camps This young child hides under the cover of endless white nylon tent sheeting from new visitors entering the camp. The hesitancy to engage soon passes and curiosity follows as he is interested to discover more about Muslim Aid. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps In Enmaa camp, Wardi takes a neighbour’s child onto her knee. She has 4 children of her own; they left Homs in 2013 after heavy bombardments and a lack of food. They travelled for 4 days to reach the border. Years on they still suffer acute hunger at times. Muslim Aid Food voucher scheme is literally sustaining and changing lives in these camps. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Taima, (Enmaa camp Lebanon) picks the very few flowers with her friends off the perimeter of the camp floor and hands them to a member of the Muslim Aid team. These acts of kindness are so incredibly powerful to see. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Zaynab currently lives in Suleyman camp in Mohamra, Lebanon in a small tent housing 15 people in two rooms. Zaynab fled Syria in 2013 and travelled through fields and mountains to reach the Lebanese border, traumatised by the fear of planes, bombs and grenades. The family are currently in great need of food and gas. Bread has become very expensive and inaffordable. In her tent was a basket of bread that was stale and mouldy. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Sumayya, Murfat’s youngest sister, peers out from their tent. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps A father attempts to create some normality by teaching his youngest son how to ride his first bike in between the network of tents and alleyways in the camp. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Malik 8 and Hazayfa 5 at Suleyman camp are amongst those fortunate to benefit from schools nearby offering classes after normal hours. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Mothers and wives are left to spend their days in the camps with memories of losing husbands fathers and sons causing in Syria and during their journey to the safety of neighbouring countries such as Lebanon and Jordan. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps It is truly amazing the defiance and resilience these children to show that they refuse to give up smiling regardless of how terrible their journey was that brought them to Enmaa camp. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Suleyman camp, Lebanon - many people have medical issues and can’t afford treatment, so cash is desperately needed to provide this support. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Murfat 3, lives with her mother and sister in a shelter provided. Their clothes, damp from the morning showers, left to dry in the porch of the tent by the air which is warm and thick with flies. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Mohammed, 2, Suleyman camp, Lebanon. There are 250,000 Syrian refugees in northern Lebanon alone. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Al Inmar camp, Lebanon. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Malaak, 11, in Suleyman camp, Lebanon. Here children are living in tents which leak in the rain and are too flimsy to shield them from the cold in winter. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps 16 yr old Homam in front of his mobile phone repair business as a result of micro-finance loan from Muslim Aid. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps A young girl looks out across the geography of Enmaa Camp and beyond to the horizon of the coastline. The 250 tents have been squeezed onto a small plot of land amongst a smart residential neighbourhood and acres of poly tunnels growing fruit and vegetables. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Hayaan, just 3 year-old, in Suleyman camp, Lebanon, makes the sign for victory or peace. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps White chalked lines replaced by empty oil drums fashioned into makeshift rubbish bins mark out the perimeter of the pitch. Hamaad, 8 years-old, likes to play football in the wasteland around the tents. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Many of Sulayman’s residents had previously been surviving on donated bags of mouldy bread and some even fasting voluntarily long before the start of Ramadan. Paddy Dowling Syrian families waiting in the shadows of Lebanon's refugee camps Sumaha, 10 years-old (Suleyman camp in Lebanon), talks to us with her friends before they leave the camp to attend a class at a nearby school. Photos Paddy Dowling

But it added that it would not give up its weapons, and warned against “the trickery of the Russian occupier or having faith in its intentions”.

Residents of Idlib who spoke to The Independent by phone said the Russia-Turkey deal had brought a degree of calm to the last rebel holdout in the country.

“There is more stability and a sense of greater security. People are feeling safer than before,” said Ahmed, who currently lives in a camp near the Turkish border and gave only his first name.

But further south, the observatory said the crackdown had “destabilised the state of security and stability” that the agreement instilled.

Support free-thinking journalism and attend Independent events

The arrests come as group’s influence is being sapped by increased Turkish involvement in the province, which has only deepened since the deal with Russia. Ankara has sought to strengthen more moderate groups to act as a bulwark against extremists, but has so far avoided open conflict.

Hayat Tahrir al-Sham has announced a number of operations in Idlib which it said were aimed at rooting out Isis sleeper cells and “collaborators” with the Syrian government. As far back as August, the group announced it had arrested 30 people who it said were attempting to reconcile with Damascus.

“Hayat Tahrir al-Sham is seeking to consolidate its power in Idlib, using the excuse that it is acting decisively against local spies of Assad, or outside powers, that are seeking to end the armed revolution,” said Nicholas Heras, Middle East Security Fellow at the Center for a New American Security.

“These arrests also send the message that it is still business as usual in Idlib, which is that nothing there can happen unless HTS grants its blessing, and that the other elements of the Syrian opposition that might oppose it are vulnerable.”

But the arrests are a recognition from the group that it is under threat.

“Hayat Tahrir al-Sham is a smart military-political actor, whose history shows a consistent willingness to assert and preemptively protect itself from any existing or potential future threats,” said Charles Lister, a senior fellow at the Middle East Institute.

“There’s a clear concern about security threats posed by reconciliation and the return of an Isis presence in Syria’s northwest. Security operations that have resulted from both of those perceived threats have resulted in widespread arrest campaigns and military operations,” he added.

The ceasefire has also given space for civil activists to protest more openly against the group. Since the Idlib deal was implemented, a number of large-scale protests have taken place across the province calling for the removal of Mr Assad, while also criticising extremist groups like Hayat Tahrir al-Sham.

In an effort to reinforce the Idlib deal, the leaders of Turkey, Russia, Germany and France are to hold a summit in Istanbul next week.