Iran shut a key border crossing with Pakistan on Sunday amid unrest in a nearby city on Friday.
Zahedan, a Sunni city in the Shia-majority Islamic Republic, saw at least 19 people killed that day.
Reports by international media said police had shot at protesters while the Sistan and Balochistan province's governor said there had been an attack on a police station.
Jaish Al-Adl separatists claimed responsibility for the slaying of a local intelligence leader during the unrest.
A source at the Pakistani Federal Investigation Agency said Iran shut the Taftan crossing, located around 55 miles (90 kilometres) from Zahedan, the capital of Sistan and Balochistan.
"They are not allowing departure movement from Pakistan into Iran," the source told Arab News.
"On Saturday, they allowed 780 people, including foreigners who wanted to cross into Pakistan, but on Sunday they completely halted all kinds of trade and pedestrian movement."
News website Iran Wire reported that a group of Baloch activists said protesters in Zahedan on Friday were railing against both Mahsa Amini's death and the alleged rape of a teenage girl by a local security official.
Amini, 22, was a Kurdish woman who died in police custody last month. Her Kurdish name can be spelled as "Jina" or Zhina".
Amini was shopping in Tehran with her family members, including her brother, when she was stopped by the morality police for allegedly wearing her hijab "incorrectly".
The authorities, who have been accused of beating her, maintain she died from "natural causes".
Communications were cut off this weekend in and around Zahedan.
Mobile phone connections were partly available again on Sunday, though the internet remained offline.