Syrian foreign minister Walid Muallem, a stalwart of Bashar Assad's government who held his job through a decade of conflict and several reshuffles, died Monday at the age of 79.

The veteran diplomat was hit with US and European sanctions early on in the conflict that has torn Syria apart since 2011 and was known for his tirades claiming that the war was the result of a Western plot.

Muallem, who had been foreign minister since 2006, started his career in the diplomatic service in 1964. In 2012, he also became deputy prime minister.

The government announcement did not specify the cause of his death, but his health was understood to have been deteriorating for some time.

His last public appearance was at the end of last week in Damascus at the opening of a conference on refugee returns. He looked weak and was helped into the hall by two men.

At the same conference, which was snubbed by most international humanitarian players, foreign attendees and Assad took part via video link.

Muallem was wearing a surgical mask and appeared to have lost weight.

In 2014, he had undergone heart surgery in Beirut.

Muallem has "continued to beat this drum of international conspiracy and has attempted to cover up the government’s horrific activities by making claims that terrorists or others were responsible,” Washington said at the time.

Muallem was one of the most recognisable figures in a Syrian government which remains very isolated internationally despite recent efforts to normalise ties with Gulf countries.

His funeral was held on Monday afternoon in the presence of a flurry of officials including deputy foreign minister Faisal Al Meqdad.

Syria’s Prime Minister Hussein Arnous saluted a "veteran diplomat who capably defended his country in international fora”.

‘Very reliable partner’

Russia, long a close ally of the government and the main foreign broker in Damascus since its war-changing military intervention in 2015, was the first nation to pay tribute to Muallem.

Mikhail Bogdanov, Russia’s deputy foreign minister, hailed Muallem as a diplomat who "understood the importance of Syrian-Russian relations”.

"We have lost a very reliable partner and sincere friend,” said Bogdanov, who was formerly stationed in Damascus. He stressed that he had been in "almost constant contact” with Muallem in the 35 years he had known him.

The foreign minister of ally Iran, Mohammad Javad Zarif, said Muallem "played an important role in serving and defending his country’s national interests and security”.

Neighbouring Lebanon, which says it hosts around 1.5 million Syrian refugees, and Oman also sent their condolences.

Muallem had replaced Farouq Al Shara, a fellow Sunni who was foreign minister for over two decades and came from the Daraa governorate, which is considered the birthplace of the revolt that erupted against the regime nearly 10 years ago.

During more than half a century in the foreign service, the unfailingly loyal Muallem held posts in Tanzania, Saudi Arabia, Spain and the United Kingdom, among other countries.

He was appointed ambassador to Romania in 1975, five years after Bashar Assad’s father Hafez came to power.

Muallem was Syria’s envoy in Washington throughout the 1990s and also played a key role in Damascus’ peace talks with Israel during that same period.

He was a father to three children.