Washington  - The White House called on Hamas to halt rocket attacks into Israel and agree to a lasting ceasefire as the conflict in the Gaza Strip escalated on Monday.

"In order for the violence to stop, Hamas must stop firing rockets into Israel and agree to accept a sustainable and durable ceasefire," Gordon Johndroe, the spokesman for the National Security Council, said in Crawford, Texas, where President George W Bush was vacationing.

The Israel Air Force was in its third day of a massive offensive against Hamas in response to rocket and mortar attacks by the radical Islamist militant group. Hamas declared an end to a six-month truce with Israel earlier this month.

"Hamas has once again shown its true colors as a terrorist organization that refuses to even recognize Israel's right to exist," Johndroe said.

Johndroe called on both sides to avoid civilian casualties and allow humanitarian aid into the Gaza Strip.

Bush was receiving updates on the situation and Secretary of State Condoleezza Rice was on the phone over the weekend with several of her counterparts in the region, Johndroe said. Bush early Monday spoke with Jordan's King Abdullah.

"We also remain concerned about the humanitarian situation," Johndroe said. "We ask that all parties involved to allow food and medical supplies to reach the people there." (dpa)