Iran, Syria 'form common front'
Iran and Syria say they are to form a common front to face challenges and threats from overseas.
"We are ready to help Syria on all grounds to confront threats," Iranian Vice-President Mohammad Reza Aref said after meeting Syrian PM Naji al-Otari.
Both countries are under intense US pressure, with Washington accusing Tehran of seeking nuclear weapons.
US tensions with Syria have soared since Monday's killing of former Lebanese PM Rafik Hariri in a bombing.
Many Lebanese blame the car bombing in Beirut on Syria, but the Syrian government has denied it was responsible for the blast.
The US has recalled its ambassador to Syria in protest at the attack, although it has not directly accused Damascus of responsibility.
Envoy Margaret Scobey held talks with the Syrian foreign ministry before her departure. She has not commented on the talks.
Washington is considering new sanctions against Syria because of its refusal to withdraw its 14,000 troops from Lebanon.
US Assistant Secretary of State William Burns, visiting Beirut for Mr Hariri's funeral on Wednesday, called for a "complete and immediate withdrawal".
In Tehran, Syrian Prime Minister Otri said his meeting with the Iranian leadership was taking place at a "very important and delicate time, with Syria and Iran facing numerous challenges".
Iran's vice-president said his country would stand with Syria.
"Our Syrian brothers are facing specific threats and we hope they can benefit from our experience. We are ready to give them any help necessary," Mr Aref said.
The meeting came as Iranian Intelligence Minister Ali Yunesi said the US had been flying surveillance drones over its nuclear sites.
Washington has hinted it may take military action against Iran over its nuclear programme, which is aimed at producing a bomb.
Meanwhile Israeli Foreign Minister Silvan Shalom, speaking in London, said Iran was just six months away from making a bomb.
Iran says its nuclear programme is not military.