Syria’s top diplomat and long-time foreign minister Walid al-Moalem, a staunch defender of Syrian President Bashar al Assad's crackdown on peaceful protesters that sparked a decade old conflict, died on Monday, the government said.

There were no details on the cause of death, but the 79-year old had for years been in poor health with heart problems. A source close to the Syrian government said it was widely expected his deputy, veteran diplomat Faisal Mekdad, would replace his as foreign minister.

Moalem, who was first appointed foreign minister in 2006 and was also a deputy prime minister, held a succession of top diplomatic posts, including envoy to the United States and was involved in unsuccessful negotiations with Israel in the 1990's on a peace settlement.

"He was known for his honourable patriotic positions," the government said in a statement, adding he died at dawn and would be buried later on Monday in Damascus.

The veteran diplomat saw his country's tilt further towards Iran and Russia, which have helped shore up Assad's rule and allowed the authoritarian leader to regain most of the territory he once lost to insurgents.

Moalem, from a Sunni family from Damascus, publicly defended Moscow and Shi'ite Iran's growing military role, backed by its proxies in Syria, which many Syrian opponents of Assad labelled as an occupation and blamed for fuelling sectarian tension in a Sunni-majority country.

"I am ready to be one of Hassan Nasrallahʹs soldiers," Moalem said in August 2006, referring to the leader of the Iranian-backed Lebanese militia Hezbollah, which has in recent years sent thousands of its members to fight alongside Assad's forces.

Syria erupted into civil war nearly a decade ago after Assad in 2011 began a crackdown on protesters calling for an end to his family’s rule.

Moalem accused the United States and others in the West of fuelling his country's unrest and labelled insurgents "terrorists" in a conflict that has killed hundreds of thousands and led to the exodus of millions of refugees.

The veteran diplomat's last statements attacked the Caesar Act - the toughest U.S. sanctions yet against Damascus which came into force last June, saying they were meant to starve Syrians. He vowed that his country would get economic help from Iran and Russia to soften its blow.

Washington says the goal of the new sanctions is to hold Damascus to account for war crimes and deter it from further pursuing the war. The sanctions exempt humanitarian aid.