UNITED NATIONS — Members of an international steering group advancing the diplomacy between Israel and the Palestinian Arabs denounced yesterday Jerusalem’s declared intention to cut off electricity and fuel to the Hamas-controlled Gaza Strip.

As the so-called Middle East Quartet called on Israel to continue providing “essential services” to Gaza, one of its principal members, Russia, denied that weapons it sold to Syria reached Hezbollah illegally in Lebanon and were used in last year’s war against Israel. The three other members of the Quartet are America, the European Union, and the United Nations.

Secretary of State Rice, meanwhile, indicated to reporters yesterday that Syria is likely to be invited to an upcoming Washington summit of Arab countries and Israel, where she appears to be raising the stakes beyond issues Israel is willing to discuss.

Ms. Rice said that at the Washington summit, scheduled for November, issues such as the final outline of the borders between Israel and a future Palestinian Arab state, control over Jerusalem, and a solution for Arabs who live in other countries as Palestinian refugees would be placed on the agenda. “Of course we will have to discuss the core issues,” Ms. Rice said at a press conference after the Quartet meeting. But in recent bilateral negotiations between Prime Minister Olmert and President Abbas, as well as in meetings of lower-level Palestinian Arab and Israeli officials, no agreement has been reached over which of the core issues, if any, will be discussed in Washington, an Israeli Foreign Ministry official told The New York Sun yesterday, speaking on condition of anonymity.

In an indication of the disconnect between the international nature of the Quartet and the bilateral diplomacy, the Quartet members were joined last night by Arab leaders for an “iftar” meal, ending a day of fasting for Ramadan. Representatives of the major regional players, including Saudi Arabia and Syria, were present, while the Israeli foreign minister, Tzipi Livni, and the Palestinian Arab prime minister, Salam Fayyad, who met earlier for a one-on-one meeting in a Manhattan hotel, were not invited.

In its statement yesterday, the Quartet said it “agreed on the importance of continued emergency and humanitarian assistance” to Gaza “without obstruction.” Israel said that in response to a barrage of rocket fire from Gaza into its territory, it was weighing an interruption of electricity and fuel supplies to the Hamas-controlled area. The Quartet statement also “noted its grave concern” over the rocket fire.

The Russian foreign minister, Sergey Lavrov, said his country carefully considers the “balance of power” before approving weapons sales to the region. Mr. Lavrov denied any knowledge that rockets and other Russian weapons sold to Syria ended up in the hands of Hezbollah, as several press reports in Israel maintained.

“We haven’t received any facts” on such weapons transfers, he said, though he added, “We spoke about this with our Israeli colleagues.”

The Israeli official told the Sun, however, that Israel has complained to officials in Moscow about Russian weapons in the hands of Hezbollah, but the Russians have disputed the validity of the Israeli data and have asked repeatedly for more “proof.”