Iranian Vice-President Muhammad Reza Aref said in Tehran after meeting Syrian Prime Minister Naji al-Utari on Wednesday that both countries were ready to help "on all grounds to confront threats".
Al-Utari 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".
The announcement came barely minutes after an unknown aircraft fired a missile on Wednesday in a deserted area near the southern city of Dailam in the province of Bushehr where Iran has a nuclear power plant, Iranian state television said.
"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 20km from the city," Iran's Arabic language al-Alam said.
Accusations and claims
Earlier on Wednesday, Israel had said that Iran was just six months away from having the knowledge to build an atomic bomb while Tehran accused the US of using satellites "and other tools" to spy on its nuclear sites.
Israeli Foreign Minister Silvan Shalom said on a visit to London that he believed "in six months from today they [Iran] will end all the tests and experiments they are doing to have that knowledge."
Iran retaliated with its own claim that the US was using satellites to spy on Iran's nuclear sites, Iran's Intelligence Minister Ali Yunesi was quoted as saying on Wednesday.
"We believe the US has been spying against Iran for some time using satellites and other tools," he was quoted as saying on the official IRNA news agency, when asked about US denials that it was using drones over Iran.
Yunesi also denied allegations by Washington that Tehran was secretly trying to develop nuclear weapons. Iran says its nuclear activities are for generating electricity.
Pressure on Syria
Meanwhile, the US has stepped up political pressure on Syria by recalling its ambassador for urgent consultations to show its deep displeasure with Damascus after Monday's killing of former Lebanese Prime Minister Rafiq al-Hariri.
US officials said they were considering imposing new sanctions on Syria because of its refusal to withdraw its 14,000 troops from Lebanon.
While acknowledging they do not know who was to blame for al-Hariri's car-bomb assassination, US officials argued Syria's military presence and its political power-broking role were generally responsible for Lebanon's instability.
Syria rejects accusations it supports terrorism.