Jerusalem ? Prime Minister Ariel Sharon told the army to do whatever was needed to end Palestinian rocket, mortar and bomb attacks, and the government dismissed a call Sunday by the PLO leadership for a halt to militant violence, hours before Palestinians claimed Israeli tank fire had killed a 28-year-old man and his mother in the Gaza Strip.

“Despite the change in the Palestinian leadership, we note that those at the top have not begun any action whatsoever to halt the terrorism,” Sharon told the Cabinet at its weekly meeting. “The situation cannot continue.”

After nightfall Sunday, a tank shell slammed into a house in a Gaza refugee camp across from an Israeli settlement, killing a 28-year-old man and his 59-year-old mother and seriously wounding his father, Palestinians said.

The bloodshed has escalated tensions with the new Palestinian leader, Mahmoud Abbas, whose election last week had raised hopes for a breakthrough in Mideast peacemaking. Palestinian officials accused Sharon of undermining Abbas’ fledgling efforts to persuade militants to halt the violence.

After Sharon unleashed his military, the Palestinian Liberation Organization’s Central Committee met to discuss the rising tensions.

At the end of the meeting, the powerful PLO body headed by Abbas said the militants were only hurting the Palestinian cause and called on them to “stop all the military action that might harm our national goals and give the Israelis an excuse to obstruct Palestinian stability.”

The statement was the PLO’s strongest language against violence since the death of longtime Palestinian leader Yasser Arafat on Nov. 11. It did not specify, however, what action might be taken against militants.

Israeli media reported late Sunday that the head of Palestinian security in Gaza, Rashid Abu Shbak, told Italian TV that if the militants do not “exercise responsibility,” Palestinian security will “exercise its authority in those areas.” Palestinian officials could not verify the quotes but confirmed the tone of the remarks.

Sharon cut off contacts with Abbas after Palestinian militants killed six Israelis at a Gaza Strip crossing Thursday. The attack sparked Israeli reprisals that killed eight Palestinians in Gaza on Saturday.