GENEVA—U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov on Saturday agreed on a cease-fire for Syria that, if implemented, would include joint military targeting by the two nations against Islamist militant groups.
Mr. Kerry, speaking to reporters after on-and-off talks with his Russian counterpart that began Friday morning and stretched past midnight, said the deal reached by the U.S. and Russia aims to reduce violence and eventually move toward a political transition. But signs of a divide within the administration over the wisdom of the deal began to emerge, with skepticism at the Pentagon over whether to trust the Russians and enter any military partnership with them on the battlefield.
Beginning at sundown on Monday in Syria, Russia and the U.S. would use their influence on the parties they support in the conflict, including the regime and opposition groups, to try to bring about seven consecutive days of relative calm at the significantly lower levels of violence that took place in February under a cease-fire that was backed by the United Nations Security Council but has since unraveled.
Once there are seven consecutive days of reduced violence and aid groups receive humanitarian access to the war-torn Aleppo area, the U.S. and Russia would begin working out of a “joint implementation center” where they would discuss how they would continue fighting the Syria Conquest Front, formerly known as the al Qaeda-affiliated Nusra Front, and Islamic State militants.
Through that process, they would develop joint targets, and once the U.S. and Russia begin coordinated airstrikes, the Syrian regime would halt its air operations in parts of Syria where opposition forces and the Conquest Front are operating.
Mr. Kerry said the U.S. and Russia believe the plan, if implemented, could be “a turning point” in the more than five-year-long civil war in which an estimated 400,000 people have been killed. “Our teams have devised what we think is a more prescriptive and far-reaching approach than we have been able to put together to date,” Mr. Kerry said.
Mr. Kerry said the plan announced Saturday included deterrents that would prevent both President Bashar al-Assad and the opposition from violating the cease-fire, but it was unclear what mechanisms, if any, were in place to hold any parties accountable.
He said the joint implementation center would allow for more-targeted strikes on the Conquest Front and Islamic State and that the U.S. would press rebel forces not to commingle with Nusra.
“There is a deterrence in that,” he said. “This new equation offers an opportunity.”
Mr. Lavrov said the Syrian regime was aware of the deal and was prepared to implement it. Mr. Kerry said opposition forces were also consulted and would be prepared to return to political talks if the regime shows “it’s serious” and if the violence decreases. He said he had consulted with Gulf Arab partners who support the opposition, and officials from those countries indicated that they would support a return to talks.
U.S. officials had hoped to announce a deal in China on the sidelines of the Group of 20 summit, but meetings between U.S. President Barack Obama and Russian President Vladimir Putin, as well as between Mr. Kerry and Mr. Lavrov, fell short of reaching an agreement.
The deal announced Saturday is the culmination of marathon diplomatic effort that began in July in Moscow, when Mr. Kerry first presented a version of the plan to ground the Assad regime’s air force in exchange for closer military cooperation as a means of bringing an end to the violence.
The officials met three times in the past two weeks and had been trading versions of the proposal. Mr. Kerry spent more than five hours consulting with officials on Friday back in Washington on the deal that was eventually was reached.
Mr. Kerry struck an optimistic tone, though he said he knew that the implementation of the accord meant more than words on paper. Defense Secretary Ash Carter and Director of National Intelligence James Clapper have recently publicly voiced concerns about the diplomacy. In China, Mr. Obama said he was unsure the U.S. could reach a deal by which Moscow would abide. The U.S. has in the past entered into agreements with Russia over Syria and Ukraine, only to have them unravel.
Meanwhile, Pentagon press secretary Peter Cook said the preliminary understanding requires Russia and the Syrian government to carry out specific steps, including the cessation of hostilities for at least seven days, before any tie-up with the U.S. armed forces is possible.
“Those commitments must be fully met before any potential military cooperation can occur,” Mr. Cook said. “We will be watching closely the implementation of this understanding in the days ahead.”
Mr. Cook said the arrangement brokered by Mr. Kerry, if implemented, could “achieve a sustained cessation of hostilities, help ease the suffering of the Syrian people and address the immediate humanitarian catastrophe in Aleppo.”
It wasn’t immediately clear whether the preliminary agreement Mr. Kerry brokered had won the wholehearted backing of the Obama administration after the round of quick-fire negotiations on Friday.
A U.S. official said Mr. Carter was among those in the Obama administration who questioned the agreement and Russia’s willingness to see through the terms of the deal. Mr. Carter in the past has accused Russia of being dishonest about its goals in Syria by claiming to go after terrorism while primarily working to regain territory for Mr. Assad and shore up the strength of his regime.
The deal comes just two days after the U.S. secretary of defense delivered a speech in Oxford, England, rebuking Russia for undermining the international order out of what he called “misguided ambition and misplaced fear.” Mr. Carter has regularly singled out Russia as one of the top five threats facing the U.S., making the possibility of any substantive military cooperation with the Russian armed forces a hard sell within the halls of the Pentagon.
U.S. officials said Mr. Carter was the only administration principal to dissent against the agreement during discussions on the matter on Friday, as Mr. Obama’s top national security advisers weighed the deal on the table before giving Mr. Kerry the green light.
Central Intelligence Agency Director John Brennan voiced skepticism that the deal would work but didn’t dissent alongside Mr. Carter, the U.S. officials said. One official said that despite the skepticism, Mr. Brennan and other cabinet members thought the deal with Russia as it stood was “worth a shot.”
A spokesman for the CIA declined to comment on Mr. Brennan’s advice.
—Adam Entous and Damian Paletta contributed to this article.
Write to Felicia Schwartz at Felicia.Schwartz@wsj.com and Paul Sonne at firstname.lastname@example.org
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