Dozens of Palestinians have been killed just hours into a ceasefire in the Gaza Strip, medics say, after Israel and Hamas agreed to a 72-hour pause in fighting. According to reports from a Rafah hospital, at least 40 people were killed on Friday as Israeli tanks fired shells into eastern Rafah.

There was an immediate lull in fighting as the truce began at 8am local time (05:00 GMT) on Friday. However, less than three hours later, medics reported deaths in the south of the Palestinian territory.

Al Jazeera’s Nicole Johnston, reporting from just east of Khan Younis in the south, reported “a very regular thud of shells from Israeli tanks”.

There were also rocket alarms sounding in Israel’s Eshkol region, signalling that rockets had been fired from Gaza. Gunfire, reportedly from snipers, could be heard east of Gaza City.

Al Jazeera’s Imtiaz Tyab, reporting from the eastern district of Shujayea district, said “a few minutes ago, about a kilometre from where I’m standing, there was a bang and we saw a large plume of smoke. We can only assume that it was either an Israeli air strike or a drone strike.”

Before the beginning of the ceasefire, 14 people were killed in the Gaza Strip, according to medics. For its part, the Israeli army said five of its soldiers had died in mortar fire near the Gaza border.

Hopes of an end to the bloodshed had risen early on Friday after US Secretary of State John Kerry announced that Israel and Hamas had agreed to a joint UN-US ceasefire proposal. Both sides swiftly confirmed their commitment to the truce, after 25 days of bloody confrontation.

While the proposal was accepted by Hamas, a spokesman stressed it was dependent on Israel reciprocating.

“Hamas and all the resistance movements have accepted a 72-hour humanitarian ceasefire from 8:00am on Friday which will be respected by all these movements if the other party also observes the ceasefire,” Fawzi Barhum was quoted as saying by the AFP news agency.

At least 1,464 Palestinians, most of them civilians, have been killed since Israel launched its offensive. Sixty-four Israeli soldiers have been killed, in addition to three civilians killed by rockets fired from Gaza.

Hours before the ceasefire was announced, Israeli Prime Minister Netanyahu, facing international alarm over a rising civilian death toll in Gaza, said he would not accept any truce that stopped Israel from completing the destruction of tunnels dug under the border by Palestinian fighters.

According to a statement by Kerry and UN Secretary-General Ban Ki-moon, forces on the ground would remain in place during the ceasefire. Israel and Palestinian delegations in the meantime will travel to Cairo for separate negotiations to reach a more durable ceasefire, the statement said. A senior US State Department official said talks could start as early as Friday, depending on how long it takes the parties to reach Cairo.

“Our understanding is that the Israelis will make clear to the UN where their lines are, roughly, and they will continue to do operations to destroy tunnels that pose a threat to Israeli territory that lead from the Gaza strip into Israel proper as long as those tunnels exist on the Israel side of their lines,” the official added.

Hamas has already said it would not accept such a condition.

“The ceasefire is conditioned with Israeli forces stopping all military operations and activities on the ground,” said Hamas spokesman Ghazi Hamad told Al Jazeera from Beirut. “It’s our right to defend ourselves and to take measures…to stop any aggression.”

Israeli and Palestinian negotiators heading to Cairo for formal talks will do so at different times: the Palestinians are expected to leave Friday mid-day, and the Israeli side after the Jewish Sabbath, on Saturday evening.

Twelve Palestinians form the delegation heading to the Egyptian capital. Three of them will travel from Gaza, and the rest from the occupied West Bank and elsewhere in the region.

The delegation will include five Hamas members and two representatives of the Palestinian Authority and Fatah. Palestinian President Mahmoud Abbas will not be heading to Cairo, but he was involved in picking the delegation members. AL JAZEERA