An explosion in south Iran, initially reported as caused by a missile, was blasting work during the construction of a dam, a senior military officer confirmed to state television tonight.
"What happened was only a natural part of building work. These were heavy blasts carried out for the construction of the dam," said Ali Reza Afshar, deputy to the chief of staff of the armed forces.
Earlier reports on Iranian state television had suggested a missile had been fired from an aircraft near the port city of Dailam. A later report sugested the explosion had been caused by a falling fuel tank from an aircraft.
The reports said the explosion was heard in a deserted area near the southern city in the province of Bushehr where Iran has a nuclear power plant.
Senior Israeli security sources said Israel's military was not involved in any explosion.
Earlier, Iran's Intelligence Minister Ali Yunesi said the US has been flying unmanned spy planes over the nuclear sites.
"A powerful explosion was heard this morning on the outskirts of Dailam in the Bushehr province. Witnesses said that the missile was fired from an unknown plane 20 km from the city," the Arabic language Al-Alam said.
Iran's Russian-built 1,000-megawatt nuclear reactor, its only nuclear power plant, is due to start operating in Bushehr province in late 2005.
Iran and Syria, both locked in rows with the United States, said earlier today they will form a common front to face challenges and threats.
"We are ready to help Syria on all grounds to confront threats," Iranian Vice-President Mohammad Reza Aref said in Tehran after meeting Syrian Prime Minister Naji al-Otari.
Mr Otari told reporters: "This meeting, which takes place at this sensitive time, is important, especially because Syria and Iran face several challenges and it is necessary to build a common front".
Washington has branded Iran part of an "axis of evil" along with pre-war Iraq and North Korea and accuses Tehran of seeking nuclear weapons.
Iran says its nuclear programme is solely for electricity generation. US President George W. Bush has dubbed the country "the world's primary state sponsor of terror" and has warned the United States could use military action to prevent it acquiring a nuclear bomb.
Syria rejects accusations it supports terrorism.