People gather to protest over high cost of living in Tehran, Iran on December 30, 2017.

Two protesters taking part in demonstrations roiling Iran were killed at a rally overnight, authorities said Sunday, the first deaths attributed to the ongoing protests as the government blocked access to a popular messaging app used by activists.

The demonstrations, which began Thursday over the economic woes plaguing Iran, appear to be the largest to strike the Islamic Republic since the protests that followed the country's disputed 2009 presidential election.

They were fanned in part by messages sent on the Telegram messaging app, which authorities blocked Sunday along with Instagram.

In Doroud, a city some 325 kilometers (200 miles) southwest of Tehran in Iran's western Lorestan province, protesters gathered for an unauthorized rally that lasted into the night Saturday, said Habibollah Khojastepour, the security deputy of Lorestan's governor. The two protesters were killed in clashes at the rally, he said.

"The gathering was to be ended peacefully, but due to the presence of the (agitators), unfortunately, this happened," Khojastepour said.

He did not offer a cause of death for the two protesters, but said "no bullets were shot from police and security forces at the people."

Videos circulating on social media late Saturday appeared to show fallen protesters in Doroud as gunshots sounded in the background. The Associated Press could not immediately verify the footage.

Thousands have taken to the streets of cities across Iran, beginning on Thursday in Mashhad, the country's second-largest city and a holy site for Shiite pilgrims.