Police in Israel are on the hunt for two suspected terrorists as an apparent bomb explosion aboard a civilian bus in Tel Aviv injured at least 21 people.

The terror attack was the first of its kind in Tel Aviv since 2006.

According to the latest casualty reports, one of the passengers, a teenager, was seriously injured, while another, also a teenager, sustained moderate injuries. The rest were lightly wounded, and at least six have already been released from the hospital.

The bomb, which exploded around noon local time on bus number 142, is believed to have been hurled onto the bus inside a backpack. A second, unexploded device was reportedly found on the same bus.

A suspect who was arrested shortly after the attack was released, and police say at least one terrorist may be on the loose in the area, and is being considered armed and dangerous.

No organization has officially taken responsibility for the attack, though Al Jazeera reported celebratory gunfire in Gaza City following news of the explosion.

A Hamas spokesperson who spoke with the news outlet called the attack "a natural event that will take place if Israel attacks Gaza."

Meanwhile, Israel and Palestinian militants continued to exchange violence as Israeli airstrikes were immediately met with rockets being fired from Gaza on neighboring towns.

The Palestinian death toll since the start of the conflict currently stands at 139; five Israelis were also killed, including one IDF soldier.

Despite the escalation, truce talks continue, with Secretary of State Hillary Clinton scheduled to meet with Egyptian President Mohamed Morsi who has been spearheading the ceasefire negotiations. Israeli sources say they hope to reach an agreement later today.

[photo via AP]