Islamic militants on Thursday fired mortars and rocket-propelled grenades at Lebanese troops as they deployed outside a Palestinian refugee camp in southern Lebanon, forcing hundreds of civilians to flee, security officials said. The soldiers fired back at the Jund al-Sham militants in an exchange that lasted about 10 minutes outside the Ein el-Hilweh refugee camp near the southern port of Sidon, the officials said, speaking on condition of anonymity because they are not authorized to speak to the media. There was no immediate word of casualties. It was not clear why the Jund al-Sham, an extremist Muslim group, opened fire. Two weeks previously there was a similar exchange between members of Jund al-Sham and the national army near Ein el-Hilweh in which two soldiers were wounded.