Palestinian Authority PM Ismail Haniyeh from Hamas, left, heads a meeting with representatives of different Palestinian factions, June 10, 2006

The Islamic militant group Hamas, which heads the Palestinian Authority, has fired rockets at Israel from the Gaza Strip, calling off a truce.

Hamas said it fired rockets at Israel in response to the killing of seven Palestinian civilians Friday in an Israeli artillery strike. The rocket fire effectively ends a 16-month old truce and threatens to spark a new wave of bloodshed.

The Israeli army says it was targeting rocket launch sites when one shell apparently went astray and hit a family picnicking on a Gaza beach. Israeli spokesman Mark Regev expressed regret over the incident, but said Israel cannot tolerate weeks of rocket attacks.

"This has to stop," he said.

The Hamas military wing says more attacks are coming, including suicide bombings in Israeli cities.