The United States has opposed arming the militants with such weapons, fearing they might end up in the hands of extremists, but Syrian opposition figures say the failure of Geneva peace talks seems to have led Washington to soften its opposition.

Pakistan makes its own version of Chinese shoulder-launched anti-aircraft missiles, known as Anza, and anti-tank rockets -- both of which Riyadh is trying to get for the militants, said the source, who is close to Saudi decision-makers, requesting anonymity.

The source pointed to a visit to Riyadh earlier this month by Pakistan's army chief of staff, General Raheel Sharif, who met Crown Prince Salman bin Abdul Aziz.

Prince Salman himself last week led a large delegation to Pakistan, shortly after Saudi's chief diplomat Prince Saud al-Faisal visited the kingdom's key ally.

Jordan will be providing facilities to store the weapons before they are delivered to militants within Syria, the same source said.

The head of the Syrian opposition, Ahmad Jarba, promised during a flying visit to northern Syria last week that "powerful arms will be arriving soon."   

Militants have long said that anti-aircraft and anti-tank rockets would help tip the balance in the battle against Assad's forces, which enjoy air superiority.

The nearly-three-year conflict in Syria has torn the country apart, killing more than 140,000 people, including some 50,000 civilians, according to the Britain-based Syrian Observatory for Human Rights.

HH/HH