PARIS — A senior State Department official said Monday that a Qaeda-affiliated rebel group was undermining the chances for a successful international effort to end the war in Syria.
By challenging moderate Syrian rebels, the group, the Islamic State of Iraq and the Levant, was forcing them to fight on two fronts and divert resources from their battle with the government of President Bashar al-Assad, the official said.
By presenting an extremist face to the world, the official said, the group was also aiding Mr. Assad’s efforts to portray the conflict in Syria as a tug-of-war between the government and jihadists.
“That has to give the regime comfort and confidence, and it will make the task of extracting concessions from the regime at the negotiating table more difficult,” said the official, who declined to be identified in accordance with the State Department’s protocol for briefing reporters on active diplomacy.
Secretary of State John Kerry, who arrived in Paris on Monday for the first of three days of Middle East diplomacy, is scheduled to meet with diplomats from 10 nations in London on Tuesday to discuss preparations for a Syria peace conference. The conference is expected to be held next month in Geneva.
A principal goal of the Geneva meeting is the establishment of a transitional government that would not include Mr. Assad.
But the senior State Department official said that fighters from the Islamic State of Iraq and the Levant, or ISIS, were hurting the peace talks’ prospects and had also hampered the flow of American and other foreign assistance across the border to the moderate resistance inside Syria.
“It has been very disruptive to our cross border efforts — very disruptive,” the official said.
As if to illustrate Mr. Assad’s growing confidence, the Syrian president recently gave an interview to a Beirut television station in which he indicated that he hopes to run for re-election next year.
Even as the Obama administration has pointed to the growing role of extremists in Syria, its policy has continued to be a target for critics, who complain that the United States has offered the moderate Syrian opposition too little, too late. American officials have not announced any major new efforts to provide arms and other forms of military support to the moderate opposition it is hoping will counteract the role of extremists.
Last month, officials notified Congress that the Obama administration was providing an additional $ 100 million in nonlethal assistance to the moderate opposition. That aid was part of a $ 250 million package that had been previously announced.
On Monday, Mr. Kerry met with Prince Saud al-Faisal, the Saudi foreign minister, over lunch. Syria was a major subject, but Mr. Kerry also intended to use the session to try to assure his Saudi counterpart that the Obama administration would not let down its guard in the newly invigorated talks with Iran over its nuclear program.
The message Mr. Kerry planned to deliver, another State Department official said before the meeting, was that the United States was “going into this with eyes wide open.”
Mr. Kerry was also scheduled to meet on Monday with Qatar’s foreign minister, Khalid bin Mohamed al-Attiyah, before briefing senior officials from the Arab League on the status of the talks between Israel and the Palestinians.
During his Tuesday meetings in London, Mr. Kerry will gather with the so-called London 11, the group of nations backing the moderate Syria opposition. Ahmad al-Jarba, the head of the political wing of the moderate Syria opposition, is expended to attend the meeting.
On Wednesday, Mr. Kerry will meet in Rome with the Israeli prime minister, Benjamin Netanyahu, whose anxiety over the nuclear talks roughly parallels that of the Saudis.
Mr. Netanyahu has expressed worries that the United States and other nations might agree to lift sanctions against Iran in return for an agreement that would place restrictions on Iran’s nuclear program but allow it to retain the capability to enrich uranium. Israel fears the enriched uranium could be quickly converted for use in a nuclear weapon that would pose a threat to its existence.
In recent weeks, American officials have not shut the door to an agreement that would allow Iran to enrich uranium to low levels as part of an arrangement in which the country would accept significant limitations and tight monitoring of its nuclear program.
Addressing the Israelis’ concerns, American officials have insisted that Iran would need to agree to “meaningful” and “verifiable” constraints on its program before sanctions were eased.
Negotiators from Iran and the world powers are to gather again in Geneva on Nov. 7 to continue their talks.