The Israeli army has sealed off the Gaza Strip, after a Palestinian attack at a border crossing. Deputy Prime Minister Ehud Olmert said on Thursday the measure was a sign of the government's determination to prevent "terrorism" after the bomb attack at a main crossing point between the Gaza Strip and Israel on Wednesday. "We have never let ourselves halt our struggle against terrorism, and we will carry on in order to prevent attacks like the one carried out on Wednesday," he said on Israeli radio. The Israeli military said in a statement: "In line with a political decision and in view of the situation, the whole of the Gaza Strip has been totally sealed off." Four Israelis were killed on Wednesday when a young Palestinian mother blew herself up at Erez border, shattering a four-month lull in attacks by the Hamas movement. "Movement (to and from Israel) will be authorised for humanitarian cases, in coordination with (Israeli-Palestinian) liaison offices," the army statement said. The military statement did not say for how long the measure would be in force, but officials had said shortly after Wednesday's attack the border zone would be shut for at least several days. **Jenin invasion*** Aljazeera correspondent in Jenin reported that the Israeli occupation forces, backed by about 20 military vehicles, penetrated into the city of Jenin on Thursday. Witnesses told our correspondent that fighters from the group of Martyr Ziad al-Amir of the al-Aqsa Martyrs Brigades were fighting the occupation forces from all directions. "The occupation forces carried out raid and search campaigns on houses in the East Quarter (Al-Hay al-Sharqi) and west of the city," said the correspondent. "Al-Aqsa Martyrs Brigades in Jenin refugee camp issued a statement in which they vowed to carry out 'painful' attacks in the heart of Israel in retaliation for the attempted assassination of Zakariya al-Zubaidi, the leader of al-Aqsa Martyrs Brigades in the West Bank", the correspondent added. **Tulkarem raided*** Also on Thursday, Israeli forces re-invaded Tulkarem refugee camp after withdrawing for one day, our correspondent there reported. "The occupation forces raided the camp, imposed a curfew and evacuated one of the residential quarters from its residents in an attempt to blow up some of the houses in the camp. "Large forces invaded the camp and others sealed off all entrances to the city", the correspondent added. **Joint operation*** Aljazeera received on Wednesday a copy of a joint announcement issued by Izz al-Din al-Qassam Brigades, the military wing of Hamas and Fatah's al-Aqsa Martyrs Brigades in which they claimed responsibility for the Erez border attack. The statement said the operation was carried out by Reem Salih al-Rayashi, a 21-year-old from Gaza city. In a televised message which was provided to Aljazeera, al-Rayashi said she had longed for martyrdom since she was in her first year of university. "I wanted to be the first Palestinian woman to carry out a martyrdom operation against the Israeli occupiers," said al-Rayashi in the televised message. **PHOTO CAPTION*** An Israeli army officer orders Palestinian workers to step back as they wait to leave the industrial area where they work at the Erez crossing between Israel and the Gaza Strip Wednesday Jan. 14, 2004. (AP Photo/Lefteris Pitarakis)