Syrian President Bashar al-Assad has defended the presence of fighters from the Lebanese Shia Hezbollah movement among the ranks of the Syrian army, saying his government had legitimately requested their help.

In an interview aired on Tuesday night on the official Hezbollah channel, al-Manar, Assad said the presence of non-Syrian fighters among the Syrian army was no justification for the presence of foreign fighters in the ranks of the rebels.

Hezbollah has led several battles against rebel groups in Syria along the Lebanese borders in the suburbs of Homs and in the mountainous Qalamoun region.

The Iranian-backed group is now heavily involved in fighting for the Damascus suburb of Zabadani.

When asked to compare Hezbollah fighting in Syria with foreign fighters supporting the rebels, Assad said: "There is a big difference. The Syrian state requested the assistance of Hezbollah.

"It was a request by the Syrian state - which is a legitimate state - in order to help defend the Syrian people."

Russian support

Assad said his major allies - namely Russia, Iran, and Hezbollah - since Syria's revolt broke out in 2011 had been "beyond loyal".

The embattled president also expressed "strong confidence" that Moscow will continue to support his regime.

"We have strong confidence in the Russians, as they have proven throughout this crisis, for four years, that they are sincere and transparent in their relationship with us," Assad said, in what was a rare television interview.

"They are principled," the president said, while "the United States abandons its allies, abandon its friends".

"This was never the case with Russia's policy, neither during the Soviet Union, nor during the time of Russia."

Assad had been asked by al-Manar's correspondent about US President Barack Obama's comments earlier this month that Russia and Iran "recognise that the trend lines are not good for Assad".

He rebuffed the statement, saying Iran, too, remained a steadfast ally.

"The power of Iran is the power of Syria, and a victory for Syria is a victory for Iran.

"We are on the same axis, the axis of resistance," the president added.

UN bias

Syria's conflict began with anti-government demonstrations in March 2011.

But after a bloody crackdown by the ruling regime, the conflict spiralled into a multi-front civil war that has killed more than 240,000 people.

In the interview, Assad reiterated that "fighting terrorism" should be the priority in any peace deal. The regime regularly labels the opposition as "terrorists".

He also accused the UN peace envoy to Syria, Staffan de Mistura, of bias for what he said was the envoy's exclusive condemnation of the Syrian army's attacks on "terrorists".

Earlier this month, government air raids on a crowded market in the Damascus suburb of Douma killed over 100 people.

De Mistura said in a statement that hitting crowded civilian markets is "unacceptable."