Syrian President Bashar al-Assad has pledged to win his country's long-running civil war while acknowledging his troops are struggling to maintain control over territory amid lack of manpower.

In a televised speech on Sunday before local dignitaries in Damascus, Assad tried to justify why the Syrian army has given up some areas of Syria, including the northwestern city of Idlib.

He said it was due to military priorities.

"It was necessary to specify critical areas for our armed forces to hang on to. Concern for our soldiers forces us to let go of some areas," he said.

"Every inch of Syria is precious."

Syria's army once had around 300,000 members, but it has been significantly reduced in size by deaths, defections, and a rise in draft dodging.

"There is a lack of human resources... Everything is available [for the army], but there is a shortfall in human capacity," Assad said.

"But that doesn't mean we can talk about collapse... We will resist... The armed forces are capable of defending the motherland."

The Syrian army has faced a series of battlefield setbacks since March: It lost most of Idlib to an opposition alliance including the Syrian al-Qaeda branch, the Nusra Front, and important areas of the southern border region to mainstream groups of the self-styled Southern Front.

The Islamic State of Iraq and the Levant (ISIL) group also seized the central city of Palmyra from the Syrian military in May.

'State of despair'

In the speech, Assad also said he supported any political dialogue to end his country's conflict, even if its effects are limited.

But he said any initiative that is not based on fighting "terrorism" will be "hollow" and "meaningless".

He said increased support from states backing opposition fighters, such as Turkey and Saudi Arabia, was the reason for recent setbacks that had created "a state of despair" among Syrians.

Syria is in a war funded by the richest and most powerful states, Assad said.

Nevertheless, he struck a defiant tone, saying there would be no compromise solutions, and he dismissed the view that Syria was heading towards partition into areas run separately by his government and the armed groups fighting him.

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The government's military setbacks have led to renewed pledges of support from Assad's main regional allies, the Shia government of Iran and the Lebanese group Hezbollah, which is fighting alongside the Syrian army.

Assad said Iran's role was limited to the provision of military experts, while publicly crediting Hezbollah for its "important" and "effective" role for the first time.

Military reversals for Assad have reduced his control beyond the main population centres of western Syria that comprise the cities of Damascus, Homs, Hama, and the coastal region forming the heartland of his Alawite sect.