JERUSALEM, Nov. 29 (JTA) — U.S. envoys attempting to broker an Israeli-Palestinian cease-fire instead got a glimpse of just how difficult their job will be. Since their arrival in Israel on Monday, the envoys — former Marine Corps Gen. Anthony Zinni and the assistant secretary of state for Near Eastern affairs, William Burns — have been confronted by Palestinian terror attacks. The latest occurred Thursday, when at least three Israelis were killed after a bomb exploded on a bus traveling from Hadera to Afula in northern Israel. At least six others were wounded, two critically, in what police said was a Palestinian suicide bombing. Prime Minister Ariel Sharon was informed of the attack as he arrived at Ben-Gurion Airport for a flight to the United States. When they heard of the bombing, Palestinians in a refugee camp near Jenin in the West Bank celebrated by firing shots into the air, according to Israel Radio. Earlier Thursday, Israel had declared a state of alert along its border with the West Bank after receiving intelligence reports that terrorists were planning to carry out a bombing attack in the country´s center. A paramedic at the scene of the attack was quoted as saying that the bus was completely blown apart, apparently from a bomb on the inside. The attack came as Zinni was holding talks with Palestinian officials in an effort to cement a truce. Palestinian officials have been concerned about the diplomatic repercussions of the series of terror attacks that have occurred during Zinni´s visit. Zinni offered his condolences to the victims´ families. "These vicious terror attacks must stop now if we are to create the environment that leads to peace," he said. The Palestinian Authority said in a statement after Thursday´s bombing that it "condemns the attack on Israeli civilians." The statement also pledged that the would "exert every possible effort to cease fire" and "follow and arrest all those who violate the leadership decision." Despite that, Israeli government spokesman Avi Pazner blamed P.A. President Yasser Arafat for the bus bombing. "These terrorist attacks are the means by which the Palestinian Authority undermines the peace mission of Gen. Zinni," Pazner said. "This is a very serious escalation, the responsibility for which is entirely on the Palestinian Authority." U.S. Secretary of State Colin Powell said he had confidence that Zinni would make headway, despite the continued violence. "Zinni will be dogged. He will be patient. We are going to try to take real, small, reciprocal steps and move forward toward this cease-fire," Powell said Thursday. The bus attack is the second Palestinian suicide bombing this week. On Monday, a Palestinian suicide bomber lightly wounded two Israeli soldiers at the Erez Crossing between Israel and the Gaza Strip. A day later, two Palestinian gunmen from the West Bank city of Jenin opened fire on civilians in the northern Israeli city of Afula, killing two Israelis and wounding dozens more. Also on Tuesday, an Israeli woman was killed in a Palestinian grenade and shooting attack on a Gaza road. "Unfortunately, there is no letup in the wave of terror against the State of Israel," Dore Gold, an adviser to Sharon, said Thursday. Not far from the site of Thursday´s bus bombing, an Israeli soldier was killed and another seriously wounded in a Palestinian drive-by shooting along the border with the West Bank. In other violence Thursday, Israeli troops killed one Palestinian man and wounded another at a West Bank checkpoint. The troops opened fire on their car when the men tried to break through the checkpoint. Palestinian witnesses said the two men had been angry about the long wait at the checkpoint.