Tel Aviv bus bombing wounds at least 21 GAZA CITY -- A bomb attack on a Tel Aviv public bus Wednesday injured at least 21 people -- three seriously -- shattering the sense of security in Israel's second-largest city and raising questions about the fate of cease-fire talks underway to end the violence in the Gaza Strip. The noon-time attack took place on a bus on a busy downtown street. Early reports from witnesses said a man was seen running toward the bus, throwing a bag inside and running away. Israel police launched a massive manhunt and raised security levels nationwide, fearing additional attacks might take place. It was unclear whether the attack was related to the ongoing clashes between Israel and the Gaza-based Islamist group Hamas, but police suspected that it was a terrorist attack. In Gaza, Palestinians cheered and celebrated on hearing the news, announced from mosque loudspeakers along with Koranic songs about victory. "Israel has refused the truce and they want to escalate the violence, so we will have to escalate as well," said bank employee Hesham Akram, 27, in central Gaza City. This way, Israelis will feel more insecure so they will give in to our demands for freedom. Hamas officials did not claim responsibility for the attack, but praised it. Hamas-owned radio said the bombing was a sign that Palestinians in Israel and the West Bank were rising up to support Gazans in the clash with Israel. The bomb smashed the front window of the bus and sent bloodied passengers stumbling into the street for help. Victims were rushed to nearby hospitals. It was unclear whether the attack would affect negotiations underway in Cairo to reach a truce in the weeklong clash between Israel and Hamas. A final deal was thought to be imminent, though the conflict continued Wednesday. Once common in Jerusalem and Tel Aviv, bus bombings have been a rarity in recent years. The last bus bomb attack in Tel Aviv was in 2006, killing 11. An attack against a bus station in Jersualem occurred in 2011, killing one person. Argentina strikes paralyze capital, other cities Church of England votes against having female bishops Former Mexico mayor survives 2 assassination attempts but not third