America sends Marine on his toughest Middle East mission

A new American peace envoy will tomorrow venture into the Middle East to find that the conflict has suddenly become still more explosive after Israel assassinated one of the top commanders from the Palestinian Islamic-nationalist group Hamas and his deputy.

The extra-judicial killing of the two guerrillas in a helicopter missile strike prompted tens of thousands of Palestinians to take to the streets for the funeral procession, chanting "Sharon, wait, revenge is coming soon."

They also prompted accusations in the Arab world that Israel's Prime Minister, Ariel Sharon, is systematically trying to undermine the latest international efforts to establish calm.

Their assassinations were among a dozen Palestinian deaths, half of them children, within a 48-hour period, which began only a few days after Colin Powell, the US Secretary of State, outlined his vision for peace in his long-awaited policy speech on the Middle East. In it, he declared that he was sending a former US Marines general, Anthony Zinni, to the region as his envoy.

General Zinni has served as commander-in-chief of US Central Command, and has seen diplomatic and military action in many of the world's trouble spots, ranging from Somalia to Central Asia and the Persian Gulf. But – if the US is serious about restoring peace negotiations rather than merely calming the region down in the name of the Afghanistan war – he now faces an unusually difficult mission. He is expected to arrive, with his fellow envoy William Burns, the Assistant Secretary of State, tomorrow.

The mood in the occupied territories suddenly became even more tense and angry after five boys – aged between seven and 14 – were killed in an explosion in the Gaza Strip on Thursday, which Palestinian officials blamed on an Israeli booby-trap. But the Israeli armed forces raised the temperature further by assassinating Mahmoud Abu Hanoud, head of Hamas's military wing in the West Bank, which has carried out numerous attacks on Israelis – including suicide bombings – although these have been scaled down sharply since 11 September. Israel's death squads have twice tried to assassinate him before. The helicopter missiles which blasted his car near Nablus also claimed the lives of his deputy, Ayman Hasaikah, and one other Hamas activist.

If General Zinni is to make any difference – and this will means quelling growing Arab suspicions that Mr Sharon has no interest whatever in peace-making but wants to aggravate the conflict – he will have to take a far tougher line on the ground than his boss. In his speech on Monday, Mr Powell used deliberately loose and anodyne terms to lay out his "vision" in which two states, Palestine and Israel, live peaceably side by side. But he offered no concrete proposals for achieving this goal, and tip-toed around the most important issues. Take, for example, the Israeli settlements built in the West Bank and Gaza in contravention of the Fourth Geneva Convention and the Oslo accords.

US diplomats acknowledge this issue played a key role in generating the Palestinian disillusion and anger that led to the intifada last year. At the end of 1993 – the year of the signing of the Oslo accords – there were 115,700 Jewish settlers in the occupied territories, according to Peace Now, an Israeli pressure group. In the years that followed, their numbers rose by 83,760. More than 20,000 new homes were built on the Arab land from which Israel was supposed to be negotiating withdrawal.

And the construction continues, despite a demand for a total freeze in the report by former senator George Mitchell which is represented by diplomats as the only path back to a ceasefire and talks. Since the election of Mr Sharon, a lifelong champion of settlements, another 25 settlements have been begun in the West Bank.

America has watched from the sidelines, occasionally protesting but without results. Mr Powell now says that settlement building "pre-empts and prejudges the outcome of negotiations and in doing so cripples chances for real peace and prosperity", and called for a halt. But the world has heard this from the US before.

Indeed, there is convincing evidence that the US has no interest at present in reviving substantive peace talks in the Middle East but simply wants to keep the region quiet. That means avoiding ruffling the feathers of Mr Sharon, while at the same time sending reassuring messages to the Arab and Islamic world. The performance of General Zinni will be the test. If he fails to play hardball, the conflict is only likely to get worse.