(Adds comments from Hamas leader)
By Nidal al-Mughrabi
GAZA, June 17 (Reuters) - An Egyptian-brokered ceasefire between Israel and Palestinian militants in the Gaza Strip that could ease a crippling Israeli blockade of the coastal territory will begin Thursday, Egypt and Hamas said.
The announcement of the ceasefire came on a day when Israel killed six militants in air strikes in Gaza. The ceasefire aims to end rocket and mortar bomb attacks on Israel from the coastal enclave and Israeli raids and air strikes in the territory.
"Both sides have pledged to halt all hostilities and all military activities against each other," Egyptian Foreign Ministry spokesman Hossam Zaki said in Cairo Tuesday, after weeks of separate talks with Israel and Hamas.
Khaled Meshaal, leader of the Islamist group, said a lasting truce would be good for 1.5 million Palestinians who have suffered from the blockade, but warned Israel that any violation of the deal would not go unanswered by Hamas.
"If you go back, we go back. The resistance factions are not in a weak position, they are in a strong position... We are a people with a cause and we will not be broken by aggression or invasion," Meshaal told Reuters during a visit to the United Arab Emirates.
Confirming details provided to Reuters by a Palestinian official in Gaza on Tuesday, Zaki said the truce would go into effect at 6 a.m. (0300 GMT) on Thursday.
Hamas leader in Gaza Mahmoud al-Zahar told a news conference in Gaza City that the truce was intended to last six months. Israel has said it would continue preparing for possible large-scale military action should a truce fall apart.
Israel’s Defence Minister Ehud Barak struck a more cautious tone but said Israel would give it every chance.
"It’s early to herald a ceasefire, and even if it were to happen ... it is difficult to estimate how long it will last. The test will be in the implementation but it is important to give it a chance," Barak said in a speech north of Tel Aviv.
The Israeli defence ministry said one of its senior officials, Amos Gilad, was flying to Cairo later Tuesday to be updated on the progress of the truce negotiations.
Senior Hamas leader Ismail Haniyeh said his group believed the ceasefire would hold and help those living in the coastal enclave: "We believe that what was agreed upon will last and the Palestinian people will see the fruits of their endurance."
The White House had no comment on reports of the truce.
U.S. officials, who reject contact with Hamas because they view it as a terrorist organization, dismissed suggestions they were being eclipsed as peace brokers.
"We’ll see first of all whether there is actually an agreement," State Department spokesman Tom Casey said. "Even if this is a true report, I think, unfortunately, it hardly takes Hamas out of the terrorism business."
Israeli and Palestinian officials said earlier that under any truce accord, the blockade Israel imposed on the Gaza Strip after Hamas seized the territory a year ago from Palestinian President Mahmoud Abbas’s more secular Fatah faction would be eased gradually and partially.
Israel has allowed in humanitarian aid but has cut back on the supply of non-essential goods, such as construction materials, as well as fuel, saying Gazans could not expect to lead normal lives while Israelis were under rocket attack.
"If Hamas keeps the ceasefire, we can gradually deliver more goods and supplies," an Israeli official said.
Any commitment to the amount of supplies Israel would allow into Gaza would be kept "vague on purpose," he said, and the enclave’s main crossing to the outside world, the Rafah terminal along the Egyptian frontier, would remain closed for now.
The Israeli official said Rafah could reopen only if there was "significant progress" on the release of Israeli soldier Gilad Shalit who was abducted by Gaza militants in a cross-border raid two years ago.
A Palestinian source familiar with the ceasefire talks said operations at the Israeli-run Karni and Sufa crossings would increase three days into the truce, the flow of goods set at 30 percent of the levels before Hamas took over the Gaza Strip.
Ten days after the truce begins, Israel would ease limitations at Karni and Sufa, the source added, although some restrictions on certain goods would remain in place. (Additional reporting by Dan Williams in Jerusalem, Cairo bureau, Lin Noueihed and Ahmed Jadallah in Abu Dhabi; Writing by Jeffrey Heller and Joseph Nasr; Editing by Jon Boyle)