ISTANBUL—Turkey’s stepped-up military campaign to crush Kurdish insurgents has reduced some urban neighborhoods in the southeast of the country to battle zones, raising fears the conflict could escalate and spread elsewhere in the country unless peace talks resume.

Since the government last week declared what it called a “decisive” campaign to end five months of limited violence between Kurds and government security forces, young Kurdish militants in the cities of Diyarbakir, Cizre, Silopi and Nusaybin have been targeted by Turkish tanks, helicopters, artillery and snipers, according to local residents and news reports from the region.

Militants in the mainly Kurdish cities have erected barricades to seal off neighborhoods they’ve declared outside the authority of the Turkish state, and are using AK-47s, rocket launchers and homemade bombs to defend the enclaves, these residents say.

Turkish officials said Wednesday that about 170 Kurdish militants and at least 11 members of Turkey’s security services have been killed since the government’s announcement last week.

The rising death toll has raised concerns among human-rights groups, the U.S. and the European Union that the fighting could expand beyond southeastern Turkey and become more indiscriminate if both sides fail to heed appeals by Washington and Brussels to stop fighting and return to negotiations.