Demonstrations were also under way in the south and the north of the coastal strip. Several smaller protests were also staged in the West Bank.
In a related development, Khalid Abu Hilal, a spokesman for the interior ministry, said Sayeed Siyam, the Palestinian interior minister, ordered Rashid Abu Shbak, head of internal security, to arrest Jon Muslih, a leader of al-Aqsa Martyrs Brigades, the military wing of Fatah, for allegedly threatening the prime minister, foreign minister and interior minister.
Hamas has rejected Abbas's call for elections, warning that it amounted to a call for "civil war" and vowed to fight the measure by bringing its supporters into the streets.
"Oh, Abu Mazen, oh spy!" chanted Hamas supporters, some of them masked and carrying the green flags of the movement and portraits of prime minister Ismail Haniya, in Gaza City.
"No, a hundred times not to early elections!" "Abu Mazen's call is a provocation and a coup d'etat against legitimacy and democracy," a Hamas spokesman, Ismail Radwan, cried to the crowd, referring to Abbas by his widely used monicker.
"The government is not responsible for the boycott" of the international community."
Abbas said he decided to call for early presidential and parliamentary elections to resolve an unprecedented political crisis with ruling Hamas.
"I decided to call for early presidential and legislative elections," Abbas said to applause during an eagerly awaited speech in Ramallah on Saturday.
"Basic law stipulates that the people are the source of power. "Let the people have their say and decide. "I will talk as quickly as possible with the central elections commission to launch the preparations for the ballot."
|Abbas said he called for early elections to|
resolve the current political crisis
Abbas dismissed warnings that the early polls would lead to civil war between the Palestinians.
He said: "Despite the suffering, the pain, the confrontations whoever is responsible for them, we will not allow ourselves to sink into a civil war.
"Palestinian blood will rest a border that will not be crossed."
Reviving the PLO Abbas expressed determination to keep the Palestinian Liberation Organisation as the only legitimate representative of the Palestinian people.
"Those who talk about the illegitimacy of the PLO's executive committee are operating under its umbrella abroad."
The governing Hamas movement immediately rejected Abbas's announcement.
Wasfi Kabha, the minister of prisoners affairs, said: "Our priority is to form a national unity government. It is the only solution. We reject anything which complicates the Palestinian situation."
Hamas, which surprised Fatah to win parliamentary elections in January, had earlier said it would regard any call for fresh elections as a coup. Abbas said he called for early elections to resolve the current political crisis.
A senior aide to Abbas said on Saturday that early elections could be held until the middle of next year for legal and technical reasons.
Saeb Erekat, a former negotiations minister, said Abbas first had to issue a presidential decree covering the early parliamentary and presidential polls. After that, voter rolls would need 90 days to be updated.
He said: "Technically, the elections cannot be held before mid-2007."
Abbas has also decided to appoint a new leadership committee for his Fatah Party, in apparent preparations for the elections, his office said.
Hamas has called for a demonstration after sunset prayers in Gaza City to condemn the call for early elections.
Several Palestinian faction leaders based in Syria have also rejected Abbas's decision.
"Any step outside the context of the laws is rejected by us all and this is not just the position of Hamas," said Khaled Meshaal, Damascus-based Hamas leader.
"The position that we have expressed today is the position of the 10 Palestinian factions whose history, performance and weight on the ground is well-known."
Ramadan Shallah, Islamic Jihad leader, who met with Meshaal in Damascus, urged Hamas and Fatah to reach an agreement, calling Abbas' decision "lawless".
"We believe that such a call will regrettably take us to the unknown," Shallah said in an interview to Al Jazeera.