WASHINGTON (AFP) - US Secretary of State John Kerry Sunday blamed Hamas for the continuation of the conflict in Gaza, saying the Islamic militants were refusing all ceasefire efforts.

"They've been offered a ceasefire and they've refused to take the ceasefire," Kerry told ABC television, adding that Hamas has "stubbornly" refused efforts to defuse the conflict "even though Egypt and others have called for that ceasefire."

By its actions Hamas had "invited further actions" by the Israelis to stop the rocket fire from the Gaza Strip into southern Israel, Kerry said.

"It's ugly, obviously, war is ugly. And bad things are going to happen. But they need to recognize their own responsibility," he added, referring to Hamas.

He urged Hamas to "be responsible and accept... a multilateral ceasefire without conditions".

More than 60 Palestinians were killed Sunday as Israeli forces pounded northern Gaza, sending thousands more fleeing in terror in the deadliest assault on the enclave in five years.

Sunday's bloody toll prompted urgent efforts by the International Committee of the Red Cross to broker a temporary ceasefire to allow paramedics to evacuate the dead and wounded in a deal accepted by both sides.

Blitzing the Sunday television talk shows, Kerry said he was planning to meet up with UN chief Ban Ki Moon who is headed to the Middle East to lend his efforts to seeking a truce.

"We're working on the idea of a ceasefire," Kerry told CNN television, adding that President Barack Obama was to speak later Sunday with Israeli Prime Minister Benjamin Netanyahu.

"Israel is under siege by a terrorist organization that has seen fit to dig tunnels and come through those tunnels with handcuffs and tranquilizer drugs, prepared to try to capture Israeli citizens and take them back to hold them hostage," Kerry said.

"No country could sit by and not take steps to try to deal with people who are sending thousands of rockets your way."