Russian fighter jets and bombers are parked at Khmeimim air base in Syria on June 18. (Pool photo by Vadim Savitsky/Russian Defense Ministry Press Service via AP)

The Obama administration has offered to help Russia improve its targeting of terrorist groups in Syria if Moscow will stop bombing civilians and opposition fighters who have signed on to a cease-fire and use its influence to force Syrian President Bashar al-Assad to do the same.

The offer early this week of what one administration official called “enhanced information sharing” does not include joint military planning, targeting or coordination with U.S. airstrikes or other operations in Syria.

But it would expand cooperation beyond the “deconfliction” talks the U.S. and Russian militaries began last year to ensure their planes do not run into each other in Syria’s increasingly crowded airspace.

Defense Secretary Ashton B. Carter, who has long opposed any additional cooperation, said Thursday that if Russia would “do the right thing in Syria — that’s an important condition — as in all cases with Russia, we’re willing to work with them.”

“The Russians got off on the wrong foot in Syria,” Carter said. The stated purpose of airstrikes Russia began last fall was “to fight ISIL and . . . assist the political transition in Syria towards a post-Assad government.”

“They haven’t done either of those things,” he said. ISIL, along with ISIS and Daesh, is an alternative term for the Islamic State.

Senior administration officials declined to discuss details of the proposal, saying that publicizing the content of diplomatic talks would undermine their possible success.

“We’ve made no bones about the fact that if the Russians, with their military presence in Syria, proved to be willing to focus those efforts against Daesh, then that’s a conversation we would be willing to have,” State Department spokesman John Kirby said.

“There have been proposals offered by multiple parties,” he said. “We’re certainly not going to start laying those out publicly.”

The United States and Russia, while backing opposing sides in Syria’s civil war, co-chair an international task force that agreed early this year — along with Assad and the opposition — to support a “cessation of hostilities” and begin negotiations for a political solution that would allow the international community to turn its full attention to the fight against the Islamic State.

More than 400,000 Syrians have died in the civil war, which has also displaced half the population, with millions fleeing to neighboring countries and beyond.

The Islamic State and Jabhat al-Nusra, al-Qaeda’s Syrian affiliate, are not parties to the truce. The administration has charged that Russia and Assad’s forces have violated it by continuing to launch airstrikes and other attacks on the anti-Assad opposition and civilians, under the guise of targeting the terrorist groups.

“What has prevented us from being able to more effectively coordinate militarily is that what the Russians have been militarily doing is propping up Assad and not going after ISIL,” White House press secretary Josh Earnest said.

Russia has defended its actions, and those of Assad, by saying that U.S.-backed opposition fighters are interwoven with Jabhat al-Nusra forces, especially around the northwestern Syrian city of Aleppo.

While violations of the truce have escalated throughout Syria’s populated western third, Aleppo has become the epicenter of fighting. Jabhat al-Nusra forces are principally massed to the south of the city. While the administration has acknowledged some overlap in opposition-held areas to the north, officials charge that Russia’s principal interest in bombing there is to help Assad’s forces close rebel and humanitarian supply lines across the nearby Turkish border.

The advance of Islamic State fighters to areas close to Aleppo and other populated areas has also brought U.S. and Russian aircraft into closer proximity over the complicated Syrian battlefield. The Islamic State has rarely clashed with Assad.

In early May, as the cease-fire and U.N.-shepherded peace talks headed toward collapse, Secretary of State John F. Kerry and Russian Foreign Minister Sergei Lavrov agreed to send senior military officers to “sit at the same table” in Geneva, where they set up a center to monitor violations.

Weeks later Russia — which has long sought more coordination with the West in Syria — proposed joint airstrikes against Jabhat-al-Nusra with the U.S.-led coalition that is bombing Islamic State positions.

Although U.S. officials were dismissive, the proposal unsettled U.S.-backed opposition representatives, who feared a backroom U.S.-Russia deal. They have said they will not return to the negotiating table until the violence abates.

Kerry and other U.S. officials have remained in close contact with their Russian counterparts, trying out a series of possible initiatives to revitalize the cease-fire, including the new offer of increased intelligence sharing on terrorist positions. Kerry is “fixated” on the Syria issue, “and he will stay so,” Kirby said.

Kerry has long advocated a more robust U.S. strategy to help the anti-Assad opposition, including additional weapons systems and the possible bombing of Assad’s military assets. Internal unhappiness with the current strategy, and the humanitarian disaster the war has brought to Syria, led 51 U.S. diplomats last month to write an internal “dissent channel” appeal for U.S. military action.

While President Obama has steadily increased U.S. attacks against the Islamic State in Syria, he has rejected entreaties for more direct involvement in the civil war, saying that he does not see how it would improve the situation.

But Obama has blessed efforts to persuade Russia to change its policies, including the intelligence offer.

Administration officials believe that the Russians have no deep attachment to Assad himself but fear his removal would spark a collapse of Syrian institutions and allow terrorist expansion — something the Obama administration has said will happen if Assad remains.

In an address Thursday to Russian ambassadors gathered in Moscow from across the world, President Vladi­mir Putin said that he was “prepared to work with any future president” and was interested in closer cooperation with the United States in international affairs.

“However, we consider unacceptable the approach on the part of the American establishment, which believes that they can decide in what issues they will cooperate with us,” Putin said.

Missy Ryan contributed to this report.