WASHINGTON, July 11 (Reuters) - The Quartet of Middle East peace mediators failed to announce any progress toward reviving Israeli-Palestinian peace talks after a lengthy meeting on Monday, saying there are still gaps between the two sides.

The group, which includes the European Union, Russia, the United Nations and the United States, ended a roughly two-hour and 15-minute dinner meeting in Washington without issuing a statement.

The Quartet wants to find a way to resume talks and to avert a diplomatic showdown expected at the United Nations in September, when the Palestinians may seek wider international recognition for a Palestinian state.

There are still gaps that are impeding progress, said a senior Obama administration official who briefed reporters after the meeting on condition of anonymity. Realistically ... more work needs to be done to close those gaps.

There is a time and a place for public statements and there is a time and a place for private diplomacy, he added. We need to do more work, privately, quietly, with the parties, in order to see if we can't close these gaps.

The official declined to discuss the nature of the gaps and he said the Quartet perceives an urgent need to appeal to the parties to overcome current obstacles and find a way to resume direct negotiations without delay or preconditions.

U.S. Secretary of State Hillary Clinton hosted the dinner, which was attended by European Union foreign policy chief Catherine Ashton, Russian Foreign Minister Sergei Lavrov, U.N. Secretary-General Ban Ki-moon and former British prime minister Tony Blair, a Quartet envoy.

The core issues in the conflict include borders, security, the future of Jerusalem and Jewish settlements in territory Israel occupied in the 1967 Middle East War, and the fate of Palestinian refugees.

More than half way through his four-year term, President Barack Obama has failed to bring Israel and the Palestinians into sustained talks to end their conflict and appears all but certain to miss a September 2011 target for a framework deal.

In a May 19 speech, Obama laid down his clearest markers to date on the compromises he believes Israel and the Palestinians must make for peace and he argued that when talks resume they should focus first on the issues of territory and security.

The result of the speech, which the White House hoped might help lay the ground for a new push for peace, was more clarity on how the United States sees an ultimate peace deal but no real impetus for fresh negotiations that might deliver one.

(Editing by Philip Barbara)