Condoleezza Rice, the US Secretary of State, made an unscheduled return to Jerusalem this evening, still hoping to salvage negotiations to open up border crossing to Gaza.

Dr Rice delayed a planned departure for Asia to apply further pressure on Israeli and Palestinian leaders to find a compromise over proposals to reopen Gaza’s border with Egypt.

Dr Rice, who was celebrating her 51st birthday today, has staked the success of her Middle East tour on injecting fresh momentum into the talks.

After meeting both Ariel Sharon and Mahmoud Abbas for separate summits this morning, she flew to Jordan to meet casualties of last week's hotel bombings in Amman. Dr Rice was scheduled to fly straight on to South Korea but delayed the flight to return to Israel for further talks.

"We’re still working the issues," her spokesman, Sean McCormack, told reporters, announcing that the chief US diplomat would spend at least one more night in Jerusalem.

A deal to reopen the Rafah crossing was said to be "within sight" after this morning's talks.

Rafah remains the only direct opening to the rest of the Arab world from territory that Israel handed to the Palestinians two months ago, and the failure to negotiate its permanent opening has become a symbol of Gaza's isolation.

Earlier this month, the Israeli security cabinet approved a decision to reopen the crossing under joint Egyptian and Palestinian control, with EU observers monitoring the terminal.

But negotiations have reached deadlock over Israel’s insistence on having access to real-time surveillance feeds. The Palestinians have rejected the demand as an infringement on their sovereignty.

US officials took no pains to hide their eagerness for an agreement today. By mid-afternoon they had erected a podium flanked by two US flags in anticipation of an appearance, apparently by Rice, to announce a deal.

At 8pm tonight (1800GMT), however, the podium remained in darkness.

The Secretary of State, seen as the Republicans' best hope for the next US presidential election, made it clear she had a personal role in the drawn-out deliberations.

"I’m trying to, through my presence here and through my work here encourage the parties to get to the place that they can then start moving on actually doing the things that are anticipated in such an agreement," she said.

Dr Rice had hoped her visit would inject momentum into a peace process that has largely stalled since Israel’s historic pullout from Gaza.

Neither party has showed signs of giving ground. The visit of the US delegation was overshadowed by the killing of a senior Islamic militant by Israeli troops in Nablus, 50 miles north of Jerusalem.

Israeli troops shot dead the leader of the armed wing of the Islamist movement Hamas in the northern West Bank city of Nablus during an operation to arrest members of the radical faction.

Hamas called the dead man one of its "top explosives experts" and issued a warning to Israel:"You will soon pay for your crimes and regret every drop of Palestinian blood you have spilt."

Another Palestinian was killed and two others wounded in the Gaza Strip near the security fence with the Jewish state after Israeli troops opened fire.

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