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.
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.