Clinton had already met with Israeli negotiator Yitzhak Molho and "she'll see Erakat next week," State Department spokeswoman Victoria Nuland said.

The top US diplomat had also talked two days ago with Israeli Prime Minister Benjamin Netanyahu and separately with Palestinian president Mahmud Abbas.

"All of this is further to encouraging them to build on the exchange of letters and continue to take the next step toward the table," Nuland told journalists.

"We're trying to improve the atmosphere so that we can make progress and get them back to the table."

While direct peace talks between Israel and the Palestinians remain in deep freeze, top officials from both sides have been holding a quiet dialogue on a range of issues, including an exchange of letters between Netanyahu and Abbas.

Envoys from the Middle East Quartet met in Brussels on Friday amid calls from the Palestinians to step up action to halt continuing Israeli settlement activity.

Officials from the United States, United Nations, European Union and Russia gathered "to consult as they routinely do over the phone as well", said a spokesman for EU foreign policy chief Catherine Ashton.

"We expect full-status participation because we already have it in UNESCO and we have ties with Brazil (the host country which recognizes the Palestinian state) and with more than 130 countries," Palestinian ambassador Ibrahim Alzeben told AFP.

The issue is generating disagreement among UN delegations.

The Palestinian Liberation Organization has observer status at the United Nations and the Palestinians are pushing for full membership in the world body.

"There are discussions" on the issue and "no clarity" on how the Palestinians should be represented, said Nikhil Seth, head of Sustainable Development at the UN.

The official pointed to two resolutions applied by the UN for its meetings, one by the UN General Assembly which convened Rio+20 and grants the Palestinians observer status and another used in the past that allows the participation of observers as states in some occasions.

The final decision will be made at a procedural session when the official Rio+20 summit opens on Wednesday, Pragati Pascale, a UN spokeswoman for the conference, said.

The Palestinians have been members of UNESCO since October, a decision that was opposed by the United States and Israel.

"We are still hoping that the world will recognize our right," said Alzeben, who announced that the Palestinian delegation will be led by foreign minister Riyad al-Malki.

The Rio+20 conference, which comes 20 years after the First Earth Summit here and runs through June 22, aims to reach common ground on sustainable development that would reconcile economic growth with poverty eradication and environmental protection.