Speaking to journalists after meeting other Damascus-based Palestinian factions on Tuesday, Khaled Mashaal warned against internal fighting and called for national unity.
He said it was necessary to solve "differences through dialogue to enable the Palestinians to continue the battle of liberating Gaza and the rest of occupied Palestinian lands".
Referring to the Gaza clashes, Mashaal said: "There is foreign pressure and incitement" - alluding to pressure from Washington and Israel for Palestinian President Mahmoud Abbas to disarm Hamas.
In the worst fighting between Hamas and Palestinian police in nearly a decade, three people were killed on Sunday, including the deputy police chief in the Shati refugee camp near Gaza City.
The officer was shot in the head after he and his men ran out of bullets during a Hamas assault on their station.
A second senior Hamas figure, Abu Muhammad Mustafa, told Aljazerra that faction leaders at the talks had "denounced recent incidents and banned the use of arms to settle Palestinian internal disputes".
"As long as our land is occupied, the Palestinian people and their factions have the right to jointly resist and play a political role"
Hamas political leader
Adding that some groups in the Palestinian Authority (PA) were working with the US to tarnish the resistance movement's image, Abu Muhammad said: "We are keen to keep arms ... for defending the Palestinian people against the enemy".
He said it was the PA that was guilty of using weapons irresponsibly.
Politics and resistance
The infighting underscored the difficulties Abbas and his security forces face in trying to take control of Gaza. Since Israel's unilateral disengagement from the coastal territory last month, Hamas's public displays have challenged Abbas.
In a statement issued after the Damascus meeting, also attended by Farouk Kaddoumi, head of the PLO's mainstream Fatah movement, faction leaders stressed "the Palestinian right of resistance until all legitimate rights are achieved".
They also urged all Palestinian factions to avoid fighting over internal differences.
Mashaal warned that "no one has the right to interfere in internal Palestinian affairs even if it was the US administration".
He rejected US Secretary of State Condoleezza Rice's demand that Hamas disarm. "As long as our land is occupied, the Palestinian people and their factions have the right to jointly resist and play a political role."
Rice said last week that Hamas could not participate in Palestinian politics if it remained armed.
"You cannot simultaneously keep an option on politics and an option on violence," she said.