Senior official Moussa Abu Marzouk, warned this weekend that a planned contentious demonstration by Israeli ultra-nationalists in occupied East Jerusalem on Tuesday could spark another war between Israel and Gaza-based Hamas if it goes ahead.
The comment came days before a "Flag Day" march in Jerusalem's occupied Old City, which could raise tensions between Israelis and Palestinians.
"Our decision is already made that it is possible the war will return," Marzouk said, if Israel continues to carry out "its usual activities".
The newly installed Israeli government - which won a vote of confidence Sunday - is supposed to take a final decision on whether to grant permission for the march during a Monday meeting.
The march was scheduled for 10 May but was cancelled with Israeli bombing of Gaza and Hamas rocket fire taking place that day.
Hamas said it targeted Israel due to its ongoing aggression against Palestinians in Jerusalem and the West Bank.
Israel's bombing in the Gaza Strip killed over 250 Palestinians including dozens of children. Thirteen Israelis were also killed by Hamas and other militant groups' rocket fire.
The Israeli broadcaster Kan reported Saturday that Israeli security officials played down Hamas's warnings of further rocket attacks but said it might carry out attacks in the West Bank or launch incendiary balloons.