BAALBEK : Militants fired heavy machineguns and mortar rounds at Lebanese troops near the Syrian border on Sunday, in a second day of clashes that have killed eight soldiers.The violence, which has also killed at least two civilians, is the worst to hit the border area of Arsal since the beginning of the war in neighbouring Syria in 2011. It erupted after the detention of a Syrian man who the army said had admitted to being a member of Al-Qaeda's Syrian affiliate, Al-Nusra Front.On Sunday morning, the army said it had lost eight soldiers in the fighting. ‘Army units continued military operations in the Arsal area and its surroundings throughout the night and into the morning, pursuing and engaging armed groups,’ the military said. ‘During the battles the army lost eight martyrs and a number of others have been wounded.’The clashes began after gunmen angered by the arrest of Syrian national Imad Ahmed Jumaa surrounded Lebanese army checkpoints before opening fire on troops and storming a police post in the town of Arsal, security sources said. Two civilians were reported killed in the storming of the police post, and the gunmen were said to have taken hostage a number of policemen, though there was no immediate confirmation.Earlier, the army said two soldiers had been briefly held by the gunmen, before troops were able to free them. The army warned of the seriousness of the situation and insisted it would ‘not allow any party to transfer the battle from Syria’ to Lebanon. ‘The army will be decisive and firm in its response and will not remain silent as foreigners try to turn our land into a field for crime and terrorism, murder and kidnapping.’ The outbreak of violence sparked clashes in the northern city of Tripoli, where Sunni militants who back the Syrian uprising have regularly fought Lebanese security forces and residents from the Alawite sect who back Syria's President Bashar al-Assad.A security source said two soldiers were wounded in Tripoli. The violence in Arsal prompted the US State Department to urge all parties to respect Lebanon's policy of ‘dissociation’ from the Syrian conflict. The United States ‘strongly condemns the attack,’ spokeswoman Jen Psaki said, vowing ‘strong support’ from Washington for Lebanon's state institutions. The US ambassador to Lebanon also met with Lebanon's army chief on Sunday to express support, the US embassy in Beirut said.Lebanese Prime Minister Tammam Salam condemned the Arsal assault as a ‘flagrant attack on the Lebanese state and the Lebanese armed forces.’ He called on ‘all political forces to exercise wisdom and responsibility and to make every effort to protect Lebanon and distance it from the dangers around it.’ Arsal, which is hosting tens of thousands of Syrian refugees, has frequently been the scene of conflict with Lebanese security forces.Syria's army has launched regular air raids and shelled the area around Arsal, saying it is targeting rebels holed up in the mountainous region surrounding the town. The UN refugee agency (UNHCR) told AFP it was ‘monitoring closely’ the situation in Arsal but had no details on whether refugees had been affected by the fighting. Tensions skyrocketed in the area earlier this year with a major influx of refugees and fighters after Syrian forces backed by members of the allied Lebanese Shiite Hezbollah movement recaptured most of the Qalamun region, just across the border.Despite the regime's recapture of most of Qalamun, pockets of opposition forces, including jihadists from Al-Nusra and the Islamic State group remain in the area. Jihadists engaged in fierce clashes with the regime in the Qalamun region on Friday night, with at least 50 fighters killed, according to a Britain-based monitor. More than 170,000 people have been killed since Syria's conflict began in March 2011, and the violence has regularly spilled into neighbouring Lebanon, which is hosting more than a million Syrian refugees.