By Nidal al-Mughrabi

KHAN YOUNIS, Gaza (Reuters) - Unidentified gunmen shot dead a judge from the governing Palestinian movement Hamas near his courthouse in the Gaza Strip on Wednesday.

Hamas officials said Bassam al-Fara, 28, was a judge in a civil court but also a member of the faction's armed wing. Four gunmen shot him in the southern Gaza town of Khan Younis while Fara was on the way to work, they said.

The attack came amid spiralling tensions and violence in Gaza and the occupied West Bank between Hamas and the rival Fatah faction of President Mahmoud Abbas in the wake of failed attempts to form a national unity government.

No one claimed responsibility for the shooting. Hamas, which accuses Fatah of trying to topple its government, issued a statement blaming the killing on a Fatah "death squad".

"The seekers of the coup in Fatah bear the responsibility for all actions of chaos taking place in the Palestinian streets," senior Hamas lawmaker Mushir al-Masri told Reuters.

A Fatah spokesman, Tawfiq Abu Khoussa, criticised Hamas for blaming the once dominant faction.

"The brothers in Hamas must be accurate and not throw quick accusations before an investigation has yet to start," he said.

Internal tensions have increased this week following the killing of three young sons of one of Abbas's top intelligence officials in Gaza on Monday.

A senior official from Fatah has said the Hamas government bore responsibility for Monday's unprecedented attack on children. Hamas has angrily denied the movement was involved.

Security forces loyal to Abbas traded gunfire with Hamas policemen in Gaza on Tuesday, wounding four people.

Besides internal political unrest, Gaza is riven with clan fighting and a surge in crime following a Western aid embargo on the government that has deepened poverty.

Residents described the Fara family as one of the biggest clans in Khan Younis, one of the most volatile towns in Gaza.

The main source of the recent tensions has been the failure of Hamas and Fatah to form a unity government that Palestinians hope might end the Western boycott.

Abbas aides have said he planned to call early elections on Saturday after talks on a unity government foundered. But they said he would still leave the door open to dialogue with Hamas.

Hamas came to power after beating Fatah in elections in January. Unity talks broke down partly over Hamas's rejection of Western demands to recognise Israel.