BEIRUT - A Western-backed rebel group in northern Syria that is under pressure from al Qaeda's hardline Nusra Front has joined an alliance of mainly Islamist insurgent factions in Aleppo, a group monitoring the conflict said on Saturday.The Western-backed Hazzm movement joined the Levant Front - Jabhat al-Shamiyya - a grouping of insurgent factions formed in December in the northern province, the Syrian Observatory for Human Rights said, citing a statement from the alliance."Hazzm is under pressure because before they refused to join Jabhat al-Shamiyya and now they accept this," said Rami Abdulrahman, who runs the Britain-based Observatory, which tracks Syria's war using a network of sources on the ground.Forming the Levant Front was an attempt at unity among factions in Syria that have often fought each other as well as the Syrian army and hardline jihadist groups, undermining the revolt against President Bashar al-Assad.The alliance includes Islamic Front, an Islamist coalition which includes Saudi-backed combatants and other factions."We urge our brothers in all factions to resolve their differences with the (Hazzm) movement via the Jabhat al-Shamiyya leadership and its judicial office by appealing to sharia law of God," the statement, which was also posted on Twitter, said.Hazzm is one of the last remnants of non-jihadist opposition to Assad in northern Syria. It has been under attack from al Qaeda's Syria wing Nusra Front in both the Aleppo and Idlib provinces.Clashes began on Thursday when Nusra Front seized positions from Hazzm west of Aleppo. Northern Syria is dominated by the hardline Nusra Front and Islamic State, an offshoot of al Qaeda that controls roughly a third of Syria.Hazzm has received what it describes as small amounts of military aid from foreign states opposed to Assad, including US-made anti-tank missiles.The fight for the city of Aleppo, divided between insurgents and government forces, is seen as one of the most significant last fronts for non-jihadist forces in the country's north.