DUBAI, United Arab Emirates -- Bomb-carrying drones targeted an Iranian defense factory in the central city of Isfahan overnight, authorities said early Sunday, causing some damage at the plant amid heightened regional and international tensions engulfing the Islamic Republic.

The Iranian Defense Ministry offered no information on who it suspected carried out the attack, which came as a refinery fire separately broke out in the country's northwest and a 5.9 magnitude earthquake struck nearby, killing three people.

Iranian state television's English-language arm, Press TV, aired mobile phone video apparently showing the moment that drone struck along the busy Imam Khomeini Expressway that heads northwest out of Isfahan, one of several ways for drivers to go to the holy city of Qom and Tehran, Iran's capital.

Isfahan, some 350 kilometers (215 miles) south of Tehran, is home to both a large air base built for its fleet of American-made F-14 fighter jets and its Nuclear Fuel Research and Production Center.

A segment aired on Iranian state TV in October included purported confessions by alleged members of Komala, a Kurdish opposition party that is exiled from Iran and now lives in Iraq, that they planned to target a military aerospace facility in Isfahan after being trained by Israel's Mossad intelligence service.

Iran's theocratic government faces challenges both at home and abroad as its nuclear program rapidly enriches uranium closer than ever to weapons-grade levels since the collapse of its atomic accord with world powers.