Israeli Prime Minister Ariel Sharon (search) severed contacts with Palestinian leader Mahmoud Abbas (search) until he acts against militants, a spokesman said Friday, a day after six Israelis were killed in an attack on a Gaza Strip (search) crossing.

The Israeli leadership had initially said it would not retaliate for the Gaza attack and would give Abbas time to rein in the militants.

"Israel informed international leaders today that there will be no meetings with Abbas until he makes a real effort to stop the terror," Sharon spokesman Assaf Shariv said.

Shariv said that Israel informed officials from the United States, the European Union, Britain and the Palestinians.

Palestinian Cabinet Minister Saeb Erekat said the Israelis had told him that they were suspending all contact with the Palestinian side.

Shariv said Israel made the decision because the attack on the Gaza crossing was launched from a Palestinian Authority base.

Earlier Friday, Israel sealed off the Gaza Strip.

Thursday night's bombing-and-shooting attack at the Karni crossing, Gaza's main lifeline, marked the militants' first major challenge to Abbas, who has spoken out against violence and said he would try to negotiate a truce.

Three Palestinian gunmen were killed in the attack, and three armed groups claimed responsibility, including Hamas (search) and the Al Aqsa Martyrs' Brigades (search), which has ties to Abbas' ruling Fatah movement.

Abbas said both the Karni attack and Israeli military operations in recent days "do not benefit the peace process." An Israeli Arab legislator who met Abbas on Friday, said the Palestinian leader remains committed to persuading the armed groups to halt attacks.

However, the lawmaker, Taleb Al Sana told Israel Army Radio that Abbas was upset with Israel for holding him responsible for attacks before he has even been sworn in as Palestinian leader.

Israel and the United States had said they would judge Abbas, who was elected to replace the late Yasser Arafat (search) and is to be inaugurated Saturday, by his actions.

But Housing Minister Yitzhak Herzog warned that Israel's patience would soon run out. "Israel will not accept a reality of continuous terror against innocent civilians. Abu Mazen does not have 100 days of grace," Herzog said speaking at a funeral for a victim of the Karni attack.

In response to the attack, Israel closed the Karni and Erez crossings, leaving Gaza largely isolated. Goods flow in and out of the fenced-in coastal strip through Karni, and the Erez crossing is used by journalists, diplomats and some Palestinian workers with jobs in Israel.

The Israeli military had eased checking at Karni in recent weeks. A third major Gaza crossing near the southern town of Rafah, used by Palestinian travelers, was closed last month after an attack there killed five Israeli soldiers.

The closures renewed hardships for Palestinians just a week before a major Muslim holiday, Eid al-Adha, a time for shopping and family visits. Many Palestinians, exhausted after more than four years of fighting, grumbled about the militants targeting crossings.

Adnan al-Khalabi, who owns a small clothing store in the Jebaliya refugee camp, said he and other shopowners were expecting holiday merchandise to come in through Karni. "This operation is going to leave a negative impact on our lives," he said. "I am proud of the fighters who work for our interest, but they should think twice before choosing a target."

Abbas has said he will not use force against militants. Instead, he is expected to try to co-opt them by asking Al Aqsa gunmen, many of them former policemen, to return to their jobs, and by offering Hamas a say in decision-making. The Islamic militant group also has said it would participate in legislative elections in July.

In coming weeks, Abbas is to conduct Egyptian-brokered talks with the militants in Gaza and in Cairo. Egypt has renewed a proposal for a one-year suspension of attacks, according to a senior Hamas official, who spoke on condition of anonymity.

Sami Abu Zuhri, a Hamas spokesman, said the attack "was a message to the Israeli enemy, definitely not to Abu Mazen." He said meetings with Abbas would resume soon "to organize the Palestinian house."

But the top Hamas official in the West Bank, Hassan Yousef, said the group is ready to suspend attacks as part of a deal with Abbas. Asked about Thursday's attack, Yousef said Hamas had freedom of action as long as no agreement has been reached.

Israeli Transport Minister Meir Shetreet said Abbas' attempt at persuasion would fail and he must crack down. "There has to be zero tolerance for terrorists," Shetreet told Israel Radio. "If he (Abbas) doesn't do this, he misses a great opportunity to lead the Palestinians in a different direction."

In the attack, just before 11 p.m. Thursday, militants detonated dozens of pounds of explosives in a truck and blew out a large hole in a door in a security wall at the crossing, said Israeli Brig. Gen. Aviv Kochavi, commander in the Gaza division.

Israel intends to pull out of Gaza in the summer. Militant groups have been stepping up their attacks in recent months to try to show that they are forcing the Israelis out. A month ago, soldiers discovered a tunnel militants were digging toward the Karni checkpoint in an attempt to blow it up.

Also Friday, the Palestinian security chief announced the creation of an elite, 750 member, unit to fight crime in the chaotic Gaza Strip.

The Palestinians have been trying to rebuild their security forces, which were weakened by more than four years of fighting with Israel. Since 2000, Israel has repeatedly targeted Palestinian police installations in response to attacks by Palestinian militants.