JERUSALEM (Reuters) -- Israeli Prime Minister Benjamin Netanyahu on Sunday announced an early election for Sept. 4.

The 120 seats in the single-chamber Knesset are allocated by proportional representation to party lists, which may secure seats after passing a minimum threshold of winning at least 2 percent of the national vote.

Following are the main parties expected to contend in the next parliamentary elections:

LIKUD -- The main right-wing party, led by Netanyahu, is expected to win 30 seats according to polls. Likud is highly supportive of the settler movement and has traditionally rejected a two-state solution with the Palestinians. However, Netanyahu endorsed it shortly after taking office in 2009, but peace talks crashed in 2010 when a freeze on settlement building was not renewed.

YISRAEL BEITEINU -- A key-coalition partner in Netanyahu's government, Foreign Minister Avigdor Lieberman's ultra-nationalist party is expected to fall to 13 seats from 15. The outspoken Lieberman has often stirred up controversy, bluntly stating there was no chance of negotiations with the Palestinians leading to peace in the near future.

SHAS -- A fixture in successive governments, the ultra-Orthodox Shas party draws its support from the fast-growing community of religious Jews of Middle Eastern origin whose spiritual leader is the 92-year-old, Iraqi-born rabbi Ovadia Yosef. It is expected to fall to seven or eight seats from its current 11.

ATZMAUT -- Founded in 2011 by Defense Minister Ehud Barak after he broke away from Israel's Labour Party, latest polls say Atzmaut is not expected to pass the vote threshold and win any seats. Barak is seen as Netanyahu's closest political ally and partner in crafting Israel's stance on Iran.

LABOUR -- Opinion polls show Labour, which ruled Israel for decades but now holds only eight seats in parliament, bouncing back to second place behind Likud under new leader Shelly Yachimovich. It is expected to gain from a wave of social protests that swept Israel last summer, and take 18 seats.

KADIMA -- Polls see Israel's main opposition party and largest faction in parliament, heading for a crash in the election, falling from 28 seats to 10 or 11. Kadima replaced Tzipi Livni as leader with ex-defense minister Shaul Mofaz, but he has failed so far to inspire the public.

YESH ATID -- Formed this year by Yair Lapid, a popular TV personality who recently turned to politics, it is promoting secular, centrist politics and looks set to win about 10 seats.

HADASH, UNITED ARAB LIST and BALAD -- Parties representing Palestinian citizens of Israel, and expected to stay jointly at 11 seats.

OTHER PARTIES:

MERETZ (3 seats) a left-wing party not in the outgoing coalition and is expected to gain about two seats.

UNITED TORAH JUDAISM (5 seats) represents ultra-Orthodox Jews of Ashkenazi, or European origin, is seen winning five or six seats.

IHUD LEUMI (4 seats) and HABAYIT HAYEHUDI (3 seats), both right-wing national religious parties with the latter a member of Netanyahu's coalition. They are expected to win two or three seats each.