Jund al-Sham is a Sunni group comprising mainly Lebanese without a clear hierarchy.
After the clash, two rocket-propelled grenades were fired and sporadic gunfire broke out in the camp, in which three Palestinian civilians were wounded.
The factional force responsible for security is dominated by the Palestine Liberation Organisation (PLO), of which the Fatah movement of Mahmoud Abbas, the Palestinian president, is a principal member.
Ain el-Helweh, near the southern port city of Sidon, with more than 45,000 inhabitants, is the largest Palestinian camp in Lebanon.
In recent months, it has become the focal point of clashes between Fatah and Jund al-Sham.
Groups believed to have links with al-Qaeda have settled in Lebanon's Palestinian refugee camps in recent years, especially in Ain el-Helweh.
The camps are outside the control of Lebanese authorities, with Palestinian factions in charge of security.