US President Barack Obama has refused to condemn Israel's ongoing atrocities in the Gaza Strip despite widespread global anti-Israeli protests.

Obama instead condemned the Palestinian groups for killing Israeli soldiers.

"I think it's important to note that we have, and I have, unequivocally condemned Hamas and the Palestinian factions responsible for killing two Israeli soldiers and abducting a third almost minutes after a ceasefire has been announced," Obama said in the briefing room of the White House in Washington on Friday.

The US president also urged Hamas to commit to the ceasefire.

"I think it's going to be very hard to put a ceasefire back together again if Israelis and the international community can't feel confident that Hamas can follow through on a ceasefire commitment," he said.

President Obama promised the United States will continue to work with Tel Aviv to enable it to protect itself against Palestinian resistance fighters.

American lawmakers have approved a bill to provide $225 million in emergency aid for Israel's Iron Dome missile system.

On Friday, the Senate rushed through a legislation to provide the money for Israel's Iron Dome. Meanwhile, Republican Senator Lindsey Graham said the Senate vote is a signal to Tel Aviv that Washington is there when Israel needs it.

The Pentagon earlier announced its ammunition deliveries to Israel.

Israel has been relentlessly pounding the besieged territory for 25 days. More than 1,600 Palestinians have been killed and thousands wounded, including women and children.

In retaliation, Palestinian resistance fighters have fired rockets into Israel.

Israel and Hamas had agreed to an unconditional 72-hour ceasefire which took effect on Friday. However, Palestinian sources said Israeli forces violated the truce shortly after it took effect, killing four people in the town of Rafah south of Gaza.