RAMALLAH, West Bank – Reacting forcefully to Hamas rocket and mortar fire in the Gaza Strip in defiance of a cease-fire with Israel, Palestinian Arab leader Mahmoud Abbas dismissed his top security commanders yesterday and sent a message to the terrorists that he will not tolerate further truce violations.

Among about 20 senior officers who lost their jobs were the top two commanders, Brigadier General Abdel Razek Majaidie, chief of public security, and police chief Saeb al-Ajed, security officials said, a clear sign that Mr. Abbas is serious about enforcing the two-day-old truce.

Hamas claimed responsibility for salvos of rockets and mortars – 30 mortars and 26 rockets, one of the biggest barrages in four years of violence – aimed at two Israeli settlements in southern Gaza, Neve Dekalim, and Gedid. The Israeli military said there were no casualties. Israeli TV stations showed video of minor damage to some houses.

Hamas said the barrage was retaliation for the death of two Palestinian Arabs Wednesday. One blew himself up with a bomb he was apparently trying to plant and the other was shot dead by Israeli soldiers as he approached a settlement. Also yesterday, armed Palestinian Arabs stormed the main Palestinian Authority jail in Gaza and killed three prisoners, part of a clan feud. Mr. Abbas also took that as an affront.

“These are very dangerous developments, and they violate the legitimacy of the Palestinian Authority,” Palestinian Cabinet Secretary Hassan Abu Libdeh said. “No one can continue with these violations.”

In a two-pronged response, Mr. Abbas sent a stern warning to the terrorists after dismissing his security commanders. And he postponed yesterday’s trip to Gaza to meet with terrorist leaders.

On Friday, Mr. Abu Libdeh said, Mr. Abbas would meet with the terrorist leaders in Gaza and “inform them that there is only one Palestinian Authority and one leadership, and [he] will not accept any measures that can subject our national project to dangers.”

Mr. Abu Libdeh added, “The Palestinian Authority will not tolerate any actions that will sabotage the agreement reached with Israelis on a mutual cease-fire.”

Israel, which has linked further progress in peace talks to Mr. Abbas’s ability to control terrorists, called for an immediate end to the violence.

The office of Prime Minister Sharon contacted Egyptian, American, and Palestinian Arab officials yesterday to express concern. “We informed them we expect the Palestinians to act immediately against these attacks,” said an aide to Mr. Sharon, Asaf Shariv.

At a summit Tuesday in the Egyptian resort of Sharm el-Sheik, in the presence of the president of Egypt and king of Jordan, Mr. Sharon and Mr. Abbas declared an end to violence and military operations after four years of bloodshed.