Five Palestinians have been killed in Israeli tank fire in Rafah, southern Gaza, despite a 72-hour humanitarian ceasefire that came into effect in the Gaza Strip, according to the Palestinian interior ministry.

Pro-Hamas media also reported that 20 people were wounded in the attack. Local sources suggest the tanks opened fire over an hour after the ceasefire began.

An Israeli government's spokesman said the artillery fired in response to serious incident on the border in Kerem Shalom resulting in number of Israeli casualties.

Israel and Hamas began the three-day truce on Friday after 25 days of conflict which have claimed the lives of more than 1,450 Palestinians, mainly civilians , and more than 60 Israelis, mainly soldiers.

US Secretary of State John Kerry cautioned there were "no guarantees" that the ceasefire would bring an end to a war.