Last minute intervention from the White House, under intense pressure from Israel, led to the surprise US abstention in last night's UN security council vote calling for a ceasefire in Gaza, according to diplomatic sources.

The resolution calling for a truce was passed by a vote of 14-0, but the US abstention will weaken its impact in Israel, where signals sent from Washington are taken very seriously and where an election is approaching. The Israeli prime minister, Ehud Olmert, issued a statement this morning saying that the security council resolution was "not practical" and that the Gaza offensive would continue.

"The [Israeli military] will continue to act in order to protect the citizens of Israel and will achieve the goals that were set for the operation," said a statement issued by Olmert's media adviser. Israeli air strikes continued overnight and this morning, while Hamas launched at least 14 rockets on Fridaytoday.

America's volte-face over the UN resoltion stunned British and the French diplomats as the US had helped draft its text. The US secretary of state, Condoleezza Rice, had fiercely defended the draft in the face of heavy lobbying from Israel which was adamant it would not accept any proposal that treated it on an equal footing with Hamas, and might limit its right of self-defence against Hamas rockets.

In the drafting process, it was France that had been most resistant to a resolution, reportedly with the aim of buying time for President Nicolas Sarkozy's diplomacy, in tandem with Egypt, to bear fruit on the ground.

Once the French had been convinced, the text was negotiated with Arab League foreign ministers in New York, who wanted tougher language but who were ultimately satisfied that the ceasefire call was in the form of a resolution, which is legally binding in theory, although it was not an enforceable resolution under chapter 7 of the UN charter. The ministers had rejected an earlier proposal of issuing the ceasefire call in the form of weaker security council presidential statement.

The text of the resolution "stresses the urgency of and calls for an immediate, durable and fully respected cease-fire, leading to the full withdrawal of Israeli forces from Gaza".

It also calls for UN member states "to intensify efforts to provide arrangements and guarantees in Gaza in order to sustain a durable ceasefire and calm, including to prevent illicit trafficking in arms and ammunition and to ensure the sustained re-opening" of border crossings.

The US change of mind came at the last moment, as a result of White House intervention following a call from Olmert. Rice was overridden and in the final vote, the US abstained. In her remarks afterwards, Rice made clear she backed the resolution, saying the US "fully supports" its goals, text and objectives. She said the US had abstained because Washington "thought it important to see the outcomes of the Egyptian mediation … in order to see what this resolution might have been supporting." However, that was an argument the US had made when the text was drafted.

The incident marks the latest in a long line of issues on which the White House has overruled the state department, both under Rice and her predecessor, Colin Powell. The hard line taken in support of Israel by George Bush and his vice-president, Dick Cheney, has been maintained until the last days of the administration.

A senior European diplomat said that US abstention still represented a diplomatic victory for UN consensus.

"Before they were going to veto, so to go from veto to a vote for a resolution was maybe too far," the diplomat said.

Britain's foreign secretary, David Miliband, who had delayed his return from New York to draft the text, said it would help bolster peace efforts in the region.

"We are all very conscious that peace is made on the ground while resolutions are written in the United Nations," he said. "Our job here is to support the efforts for peace on the ground and to help turn the good words on paper into changes on the ground that are desperately needed."