AMMAN (Reuters) - The head of a new alliance of Syrian Islamist factions, including a former affiliate of al Qaeda, has promised to escalate attacks against the Syrian army and its Iranian-backed allies with the goal of toppling President Bashar al-Assad.

Hashem al-Sheikh, leader of Hayat Tahrir al-Sham, which was formed last month, also said in his first video speech that the new grouping sought to “liberate” all of Syria’s territory.

“We assure our people that we will begin our project by reactivating our military action against the criminal regime and we will raid his barracks and positions and wage a new battle of liberation,” he said.

Hayat Tahrir al-Sham, or Body for the Liberation of the Levant, was created from a merger of Jabhat Fateh al Sham - formerly al Qaeda’s Nusra Front - and several other groups.

The jihadist alliance has enlisted thousands of fighters who have defected in recent weeks from more moderate Free Syrian Army rebel groups, angered by their leaders’ readiness to engage in a peace process with Assad’s government.

Days before the alliance came into being, heavy fighting erupted in northwestern Syria between Fateh al Sham and more moderate rebel groups, threatening to further weaken the opposition to Assad in its biggest territorial stronghold.

The jihadists said they had been forced to act preemptively to “thwart conspiracies”, accusing rebels attending peace talks in Kazakhstan of conspiring against them.

Sheikh said the new alliance would form “one entity” to spearhead the military and political work of the anti-Assad forces, saying international peace efforts aimed to “abort the revolution” and reward Assad for his “crimes” against Syrians.

“We seek to bring together the Syrian arena within one entity under a unified leadership to bring down the criminal regime,” he added.

But many smaller rebel groups fearing that the new jihadist groups’ growing influence could pose a threat to their existence have turned to protect themselves by merging with the powerful Islamist Ahrar al Sham group, a rival of the former Qaeda affiliate.

Mounting tensions in several rebel-held areas have spilled over in recent days in skirmishes among hardline Islamist groups affiliated to the new alliance and some FSA groups.

FSA groups, alongside jihadist groups including those operating under the umbrella of the new alliance, however still wage joint battles against the Syrian army despite deep ideological differences and turf wars.

They launched a new military campaign in the coastal province of Latakia, a bastion of Assad’s Alawite minority against the army.