Brown: 'Amidst suffering and grief and tears, I can see a clear path to peace'
The British government has pledged to give a further £20m in humanitarian aid to crisis-torn Gaza.
The promise came as international leaders, including Gordon Brown, met in Egypt to discuss the conflict.
The prime minister said: "Too many innocent civilians, including hundreds of children, have been killed during the military offensive."
The Palestinian militant group Hamas has announced an immediate ceasefire with Israel in Gaza.
The move comes hours after a unilateral Israeli ceasefire came into effect, ending 22 days of hostilities in which more than 1,200 Palestinians have died.
Mr Brown said both sides must go further to allow negotiations to begin over a long-term settlement.
Our first priority - a humanitarian imperative - is to get food and medical treatment to those who so urgently need it
"Three weeks of tragedy must be followed by immediate action to secure a permanent peace settlement," he said.
"Amid suffering and grief and tears, I believe I can see a clear path to peace.
"This fragile ceasefire has got to be followed immediately - if it is to be sustainable - by humanitarian access, which we have asked for, by troop withdrawals, by an end to arms trafficking, by an opening-up of the crossings, by the end of rocket attacks."
There was a "clear path to peace" being created by willingness to end fighting on all sides, he added.
The summit, in the resort of Sharm el-Sheikh, was co-chaired by Egyptian President Hosni Mubarak, who has sought to broker an end to fighting with a truce plan, along with his French counterpart Nicolas Sarkozy.
United Nations Secretary General Ban Ki-moon also attended, along with senior politicians from Germany, Italy, Spain, Turkey and Jordan.
The group have now flown on from Egypt to Israel for talks with Prime Minister Ehud Olmert in Jerusalem.
Israeli soldiers are beginning to leave Gaza to return home
It is hoped the discussions will produce progress on the closure of arms-smuggling tunnels into Gaza, as well as the reopening of border points under EU monitoring.
Details were also expected to be agreed of the Royal Navy assistance offered by Mr Brown on Saturday.
The £20m of aid announced on Sunday trebles to £30m the additional support committed by the Department for International Development since the start of the latest conflict.
As well as food, medicines and shelter, it will be used to airlift injured Palestinian children to hospitals in Jerusalem and the West Bank, to support children traumatised by violence and the death of loved ones and to clear unexploded bombs and shells in Gaza, said Mr Brown.
"Our first priority - a humanitarian imperative - is to get food and medical treatment to those who so urgently need it," he said.
"We will focus our efforts on support to the UN agencies who are doing such courageous work in the most difficult environments.
"We will help transport those civilians in most need of treatment to hospitals in the West Bank. We will also support children traumatised by the violence, rebuild schools and hospitals and clear unexploded bombs and shells.
"A humanitarian tragedy must be met not just by sympathy but by an immediate mobilisation of aid."
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