Hundreds of demonstrators calling for Palestinian unity took to the streets here on Monday, a day earlier than scheduled, in an effort to prevent what they said were attempts by political factions to hijack their movement for their own agendas.

What began as a news conference by protest organizers on Monday afternoon in the Square of the Unknown Soldier unexpectedly developed into a gathering of almost 1,000 people.

They called for national reconciliation between Hamas, the militant Islamic group that controls Gaza, and Fatah, the mainstream Palestinian party that dominates the Palestinian Authority, which controls the West Bank.

Youth organizations and activists in the West Bank and Gaza began a campaign for national unity last month, mobilizing support through Facebook. They have called for mass rallies in all Palestinian cities on Tuesday.

The rivalry between Fatah and Hamas worsened in 2006 after Hamas won parliamentary elections in the West Bank and Gaza, which are separated by Israeli territory. A year later, Hamas seized full control of Gaza, routing forces loyal to Fatah and widening the divide.

Repeated Egyptian-brokered efforts at reconciliation failed. But a renewed call for unity, spearheaded by young people, seems to have struck a chord.

“We came today before we got contained,” said Asma al-Ghoul, a young woman known for her defiant stance against violations of civil rights in Gaza. “We came to pre-empt any security measures for tomorrow.”

The organizers said that anybody openly supporting a political party would have no place at the protests, and that everyone would demonstrate under a single slogan, “The people want to end the division.”

In Gaza, there have been signs that Hamas intended to try to take over the protests planned for Tuesday and have them take place under its auspices.

Asaad al-Saftawi, a protest organizer, said that the Hamas authorities had given permission to a group representing them to install a stage in the park on Tuesday and to display slogans with a Hamas tilt against the schism.

Posters reflecting the Hamas line, pasted on a wall outside the park, said that the people wanted to end the division while “maintaining national principles.” The principles, listed on the poster, include abrogating Palestinian agreements with Israel and ending the security cooperation between Israel and the Palestinian Authority in the West Bank.

A handful of Hamas spokesmen and legislators tried to hold a news conference in the park on Monday, but they could not be heard above the songs for unity blaring out of massive speakers set up by the organizers.

Hamas has said that it feared that Palestinian Authority employees would mingle in the crowds on Tuesday and turn the protests against Hamas.

Ismail Haniya, the head of the Hamas government in Gaza, said in a statement that he had ordered the Interior Ministry “to provide a suitable atmosphere in the field to make the popular protests successful.” But he reiterated that “national principles” must be preserved in any reconciliation agreement.

By Monday night, Hamas had taken over the park, setting up its own loudspeakers, and the protesters dispersed into the streets nearby.