People are fleeing a district of the mainly Kurdish city of Diyarbakir in south-east Turkey after authorities fighting Kurdish militants there expanded a 24-hour curfew zone to include five more neighbourhoods.

On Wednesday, three soldiers were killed in an attack in Diyarbakir’s historic Sur district, which has been under curfew since December as the security forces battle Kurdish militants linked to the outlawed Kurdistan Workers’ party, or PKK. The private Dogan news agency reported heavy fighting in Sur, where the military says at least 134 militants have been killed since December.

A statement from the local administrator’s office for Sur said the curfew – which bars residents from leaving homes and observers and journalists from entering to monitor the fighting – had been enlarged to enable the security forces to “restore public order” in neighbourhoods where the militants had allegedly dug trenches and set barricades and explosive devices.

Authorities have been imposing curfews in towns and districts to flush militants from urban areas in Turkey’s mostly Kurdish south-east since the collapse of a peace process with the PKK in July. The Turkish Human Rights Foundation says at least 198 civilians, including 39 children, have died in combat areas under curfew since August.

On Wednesday, Human Rights Watch raised concerns over the civilian casualties, criticising the government for not releasing numbers or facilitating urgent medical evacuations for trapped civilians.

“Many people have died in circumstances which are extremely difficult to scrutinise because of the curfews,” said Emma Sinclair-Webb, a senior researcher at the group.

On Tuesday, Turkey’s deputy prime minister, Numan Kurtulmuş, told parliament that the security forces were taking utmost care to “distinguish between the terror organisation and the civilians and to ensure that the battle is being waged within the rule of law”.

On Wednesday, more than 2,000 people were seen leaving Sur, some carrying bedding, heaters and suitcases.

Mehmet Karatay, 55, said he had moved to Sur in the early 1990s after the security forces burned down several villages in the south-east as part of the battle against the PKK. “I have 10 children,” he said. “There are thousands of miserable people like me. Where will we be going from now on?”