FACTBOX - Armed groups operating in south Lebanon

(Reuters) - At least three rockets fired from Lebanon hit northern Israel on Thursday in an attack seen as linked to Israel's offensive against Hamas Islamists in the Gaza Strip.

There has been no claim of responsibility for the rocket attack for which there are several suspects. The rockets were fired from the Hezbollah stronghold of southern Lebanon, the scene of a ferocious 34-day war between Israel and the Lebanese guerrillas in 2006.

Here are some facts about the possible suspects behind the rocket attack:

HEZBOLLAH

The powerful political and military group has thousands of well-trained fighters who stood their ground against an Israeli onslaught in 2006. The group enjoys strong support from Iran and Syria and is listed as a terrorist organisation by the United States.

Hezbollah is the dominant military force in Lebanon, stronger than any other faction or the Lebanese army. Its arsenal, estimated to be tens of thousands of rockets, sophisticated anti-tank weaponry and possibly anti-aircraft batteries is mostly supplied by Iran via Syria.

Hezbollah still maintains a stronghold in the south even after a U.N. peacekeeping force was beefed up to 13,500 along the Lebanese-Israeli border following the end of the 2006 war. The group also has heavily fortified positions in the eastern Bekaa Valley.

PALESTINIAN GROUPS

Lebanon is home to 400,000 Palestinian refugees dispersed in 12 refugee camps across the country, the largest being the Ain al-Hilweh refugee camp in the south. These camps are home to several Palestinian groups.