TEHRAN, Iran (AP) -- The number of injured from an explosion Saturday at a port in southern Iran jumped to 281, the state-run IRNA news agency reported.

IRNA quoted Mojtaba Khaledi, the spokesman of Iran's National Emergency Organization, as giving the figure.

The blast happened at the Rajaei port just outside of Bandar Abbas, a major facility for container shipments for the Islamic Republic that handles some 80 million tons (72.5 million metric tons) of goods a year.

Social media videos showed black billowing smoke after the blast. Others showed glass blown out of buildings kilometers (miles) away from the epicenter of the explosion.

Authorities have offered no cause for the explosion yet. Industrial accidents happen in Iran, particularly at its aging oil facilities that struggle for access to parts under international sanctions. But Iranian state TV specifically ruled out any energy infrastructure as causing or being damaged in the blast.

Mehrdad Hasanzadeh, a provincial disaster management official, told Iranian state TV that first responders were trying to reach the area while others were attempting to evacuate the site.

Hasanzadeh said the blast came from containers at Rajaei port in the city, without elaborating. State TV also reported there had been a building collapse caused by the explosion, though there were no immediate other details offered.

Rajaei port is some 1,050 kilometers (652 miles) southeast of Iran's capital, Tehran, on the Strait of Hormuz, the narrow mouth of the Persian Gulf through which 20% of all oil traded passes.

The blast happened as Iran and the United States met Saturday in Oman for the third round of negotiations over Tehran's rapidly advancing nuclear program.