Pentagon leaders on Monday said a proposed agreement with Moscow to expand military cooperation in Syria would hinge on the Kremlin’s support for U.S. goals there, suggesting that senior military officials remain deeply skeptical of Russia’s trustworthiness.

Speaking in a briefing with reporters, Defense Secretary Ashton B. Carter and Gen. Joseph F. Dunford, chairman of the Joint Chiefs of Staff, gave a wary assessment of the proposal that State Department leaders have been pursuing with Russia. The deal would establish new means for the sharing of U.S. and Russian intelligence on the whereabouts of extremist militants in Syria, potentially leading to the grounding of Syrian government planes and, hopefully, a reduction in civilian casualties.

If implemented, the agreement would significantly deepen the United States’ collaboration with Russia in a conflict that has fueled tensions between the countries.

Asked whether he trusted Russia to live up to the terms of a potential deal, Dunford said: “We’re not entering into a transaction that’s founded on trust. There will be specific procedures and processes in any transaction we might have with the Russians that would account for protecting our operational security.”

The proposed agreement, which would set up a joint committee that would allow the United States and Russia to share targeting information about Jabhat al-Nusra, al-Qaeda’s Syrian affiliate, has created friction within the Obama administration over the best way to reduce the bloodshed in Syria. Both countries would conduct strikes against the group.

While many officials at the State Department see the proposal as a possible path to staunching the high civilian death toll, many Pentagon officials believe the deal would reward Russia for bad behavior. They say Moscow has ignored its promises to target only the Islamic State in Syria and instead has bombed areas controlled by rebels fighting Syrian leader Bashar al-Assad. They also believe that Russia’s decision last month to strike a rebel outpost in southeast Syria that has been used by British and U.S. troops was an intentional provocation.

So far, the Pentagon has limited its contact with Russia about Syria to de-conflicting the location of U.S. and Russian aircraft.

Moscow’s decision to send troops and planes to Syria last year has proved pivotal for its ally Assad, providing new confidence to an embattled leader and allowing his forces to recover key areas. While the United States has insisted since the Syrian uprising began that Assad must step down, it has withheld military support to rebels fighting Assad and has concentrated its military efforts on fighting the Islamic State.

Carter said the discussions being led by Secretary of State John F. Kerry seek to determine whether Russia shares U.S. goals in Syria, including a political transition away from Assad and the defeat of the Islamic State.

The talks are “based on a transaction and on mutual interest to the extent . . . we’re able to identify that with the Russians,” Carter said. “They’re not based on trust.”