Syria's President Bashar al-Assad delivers a speech after being sworn in for a new seven-year term, at al-Shaab presidential palace in Damascus July 16, 2014, in this picture released by Syria's national news agency SANA. [Photo/Agencies]

DAMASCUS - Bashar al-Assad was sworn in for a new term as Syria's president on Wednesday, after an election which his opponents dismiss as a sham but which he said proved he had achieved victory after a "dirty war" to unseat him.

Once written off in the West as certain to fall, he launches his seven-year term in his securest position since the early days of the three-year-old war. Those close to Damascus say he now believes his Western and regional foes will be forced to deal with him as a bulwark against Sunni Islamist militants who advanced across northern Iraq last month.

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At his inauguration he delivered a defiant speech, vowing to recover all Syria from Islamist insurgents and warning that Western and Arab countries would pay dearly for supporting rebels he described as terrorists.

Looking calm and confident, the president of 14 years repeatedly took aim at the West and Sunni Muslim Gulf Arab monarchies who have funded and armed the rebels that have taken control of much of the north and east of his country.

"Soon we will see the Arab, regional and Western states that supported terrorism pay a high price," he said in the speech at the presidential palace in Damascus, broadcast on state TV.

"I repeat my call today to those who were misled to put down their guns, because we will not stop fighting terrorism and striking it wherever it is until we restore security to every spot of Syria," Assad said.

But with swathes of the country still in rebel hands, opponents said the speech showed Assad was delusional.

Syria's war has been the battleground for a sectarian struggle between groups supported by Sunni Muslim states including Saudi Arabia and Qatar, and Assad's government backed by Shi'ite Iran.