A bomb has exploded on a bus in the Israeli capital city of Tel Aviv, injuring more than a dozen, but also threatening to permanently derail any hopes of a cease fire in Gaza.

Israeli police are calling it a terrorist attack, but say the bomb was planted on or under the bus, and was the not the work of a suicide bomber. Reports says as many 21 people were injured, though Haartez is reporting that none of the injuries were serious and there are no reports of deaths.

One witness says the bomber entered the bus, threw the bomb toward the back and ran off, likely giving most of the passengers a chance to escape. Police have arrested one person they thought was a suspect (who was later released) though there are reports that another may be on the loose.

Reports from Gaza are that Hamas claimed credit for the attack in an announcement made over mosque loudspeakers throughout Gaza City and that news of the attack was met with celebratory gunfire from supporters of Hamas.

Even though attack was not as deadly as it could have been, it drastically changes the situation between Israel and Gaza. Despite the onslaught of rockets over the last week, there have been no terrorist attacks from inside Israel since 2006. This attack is likely to both scare and anger Israeli citizens who don't want to return to the conditions of the second intifada, during which such attacks in Tel Aviv and Jerusalem were routine. There are already concerns that this will strengthen the argument of hardliners who don't want to agree to cease fire and instead would rather push for a ground invasion that would more seriously punish Hamas and do more damage to Gaza. Just one day after it looked like there might be peace, the war may actually be about to escalate instead.

Both the White House and Secretary of State Hillary Clinton condemned the attack and reiterated their support of Israel. Clinton arrived in Cairo to meet with Egypt's prime minister today as they continue to push for more peace talks.