Explosions from mortar bombs and rocket-propelled grenades shook the town of Beit Hanoun in the early hours after a shootout for which each side blamed the other. The street fighting spread to Gaza City, leaving eight people wounded.
The violence broke out just hours after Prime Minister Ismail Haniyeh of the Islamist Hamas movement said a unity government would be announced in the next few days.
The coalition agreement reached in the Saudi city of Mecca on February. 8 had halted weeks of bloody factional fighting in which more than 90 people were killed in the Gaza Strip.
The man killed in today's shootout was identified as Mohammad al-Kafarna, a member of the Hamas-led government's Executive Force.
Hamas accused Fatah of ambushing his car.
Fatah spokesman Abdel-Halim Awad said Hamas fighters had fired first on a car carrying members of the al-Aqsa Martyrs Brigade, linked to President Mahmoud Abbas's Fatah faction.
Fighting quickly spread in Beit Hanoun as Hamas forces attacked a Fatah office and a separate security complex. The homes of two local Fatah activists were also fired upon.
Fatah security forces declared a high alert in northern Gaza, ordering their men to reinforce their positions and set up checkpoints to intercept Hamas vehicles.
Tension had risen yesterday after Fatah gunmen shot at the convoy of a Hamas cabinet minister in the occupied West Bank, and gunmen stormed the pro-Fatah Al Quds University in Gaza City, wounding a Fatah student council member.
UNITY GOVERNMENT Haniyeh said in a television interview the unity government would be unveiled on Wednesday or Thursday and a parliamentary confidence vote would be sought on Saturday.
He said differences over who would hold the powerful post of interior minister, with control over security forces, were close to being resolved but gave no details.
Haniyeh said he planned to travel with Abbas to an Arab summit in Saudi Arabia aimed at reviving an Arab initiative for peace with Israel first launched by the host country in 2002.
''We have agreed to finalise the national unity government and we will go to the summit with the government in place and, as president and prime minister, we will ask the Arab countries to support (the new administration),'' Haniyeh said.
The Saudi plan offered Israel peace with all Arab countries if it relinquished land it occupied in the 1967 West Asia war and allowed the creation of an independent Palestinian state.
If Abbas and Haniyeh both travel to Saudi Arabia it will be the first time they have appeared together on the international stage.
In Mecca last month they each headed rival groups.
Abbas was due to meet Israeli Prime Minister Ehud Olmert in Jerusalem later today, but little progress was expected.
Israeli officials said Olmert would reiterate that Israel would keep up its boycott of any new Palestinian government unless it recognises the Jewish state, renounces violence and accepts past peace deals as demanded by the United States and its partners in the Quartet of West Asia mediators.
The unity government agreement falls short of these demands.
Israeli naval vessels fired on a Palestinian fishing boat off Gaza's southern coast today, wounding two fishermen, witnesses and doctors said.
An Israeli military spokeswoman said the boat was one of three vessels suspected of trying to smuggle arms to Gaza, and that the navy opened fire after they ignored warnings to halt.
REUTERS SP PM1736