SLAVYANSK, Ukraine — Ukraine’s army on Sunday cut off the main road to Slavyansk, tightening its siege of the flashpoint eastern city, rebels in control of the town said.

AFP reporters outside the city of 160,000 people saw seven Ukrainian armored vehicles setting up a checkpoint blocking the route to the regional capital Donetsk.

“The town is completely surrounded,” a rebel spokeswoman Stella Khorocheva told AFP.

Slavyansk, which has become the epicenter of rebel activity in Ukraine’s increasingly chaotic eastern regions, has borne the brunt of a Ukrainian military offensive to regain control of more than a dozen towns under separatist control.

The military stepped up its operations around Slavyansk on Friday, launching an attack with armored vehicles and helicopters that rebels said killed at least five people in the town.

Four Ukrainian servicemen were also killed in the raid and the rebels shot down two helicopter gunships.

The fighting has taken place on the outskirts of the city. The center, in contrast, has up to now remained relatively calm.

The rebels have barricaded themselves in occupied buildings including the town hall and the SBU security services headquarters.

Locals have thrown up barricades around the center to slow any army advance.