Violence along the Gaza Strip during the past two days has raised questions about how long a ceasefire between Israel and the Islamic militant group Hamas may hold up in the Gaza Strip. Hamas militants fired a number of rockets into southern Israel after Israeli troops killed six Palestinians this week. VOA's Luis Ramirez reports from Jerusalem.

Rockets fired by militants in Gaza rained on parts of southern Israel, including the coastal Israeli city of Ashkelon. They caused no reported injuries or property damage, but shook the thousands of Israeli residents who had for months experienced a period of relative calm brought by a truce mediated by Egypt in June.

The barrage of rockets came after Israeli forces killed at least six Palestinian suspected militants on Tuesday while moving into an area of Gaza to destroy a tunnel. Israeli officials say Hamas militants were preparing to use the tunnel for abducting Israeli soldiers to Gaza.

Israel's killing of the Palestinians drew an angry condemnation from the top Palestinian negotiator, Saeb Erekat.

The official, speaking on Palestinian radio, said that if the Israelis want peace, they should not carry out attacks like the one that killed the six Palestinians, an act he described as a massacre, and an act of aggression for which there is no reason. He called for the United States to take note of what he described as a dangerous situation.

Officials describe the violence as the worst outbreak since the truce went into effect in June.

Hamas issued a statement taking responsibility for the rocket attacks, accusing Israel of violating the ceasefire. Israel denies breaking the truce. Both sides urged calm.

Meanwhile, U.S. Secretary of State Condoleezza Rice is to begin a visit Thursday to Israel and the Palestinian territories.

The United States is trying to push along peace talks that were launched at Annapolis in the U.S. state of Maryland a year ago. The negotiations aimed to reach an agreement by the end of this year, but have made little visible progress and both sides say there is no chance of a deal by New Year's.