VIENNA (AP) -- Russia-U.S. relations are at a post-Cold War low just about everywhere, except at the Iran nuclear talks.

Despite a chill over the Ukraine crisis that has spread to almost every element of their relationship, Moscow and Washington continue to find common cause on one of the most pressing issues on the global agenda - a deal to prevent Iran from being able to make nuclear weapons.

Officials on both sides credit the other with pragmatic proposals and good faith that transcends their broader differences.

For the U.S., failure to get an agreement carries the unappealing risk of involvement in a new Mideast conflict, nor does President Barack Obama want to lose out on a key plank of his foreign-policy legacy. The Obama administration has said it could strike Iran's nuclear facilities militarily should diplomatic attempts to curb its nuclear activities fail. Israel is even more upfront about threatening to launch air attacks, a move that could draw the U.S. into the fray.

The Russians also don't want a U.S.-Iran war. Gary Samore, a U.S. negotiator at the nuclear talks until 2013, says getting an agreement is in Moscow's strategic interest as it tries to limit the U.S. presence in the Middle East.

"The Russians don't like to see the U.S. going around the world, bombing countries," says Samore, who is now with Harvard's Belfer Center think tank.

To that end, the Iran talks are also serving as a conduit between Russia and America on various ways of reducing Mideast turmoil. Russian Foreign Minister Sergey Lavrov on Monday said his talks Tuesday with U.S Secretary of State Kerry in Vienna would be an opportunity "to exchange opinions on how our two countries and other countries in the region could pool our efforts" to fight the Islamic State.

The desire is mutual.

While the Russians and Americans differ on Moscow's support for Syrian President Bashar Assad, Samore said the Kremlin's backing of Assad is now secondary to a way of defeating the Islamic State.

Though the venue was the nuclear talks, Lavrov's comments after meeting Kerry reflected how they have evolved as a place to discuss general shared concerns.

The Russian said the talks were "not the main subject of our meeting." Instead, he said he and Kerry exchanged "specific opinions and ideas on how to try to make the situation more manageable" in the anti-Islamic State campaign.

Harvard political science professor Graham Allison sees the Russia-U.S. cooperation as "good evidence that where there is real shared national interest, both Putin's Russia and Obama's U.S. can see beyond the shouting over Ukraine." He likened it to the two nations' ability to sign several significant arms limitations treaties during the Cold War.

But it's not all about goodwill.

A nuclear deal may serve Russia's own needs on a strategic level, and work against the United States. It could strengthen Tehran as a regional power allied with Moscow, both as a proxy backing the Syrian government and as a rival to U.S-backed Saudi Arabia in the struggle for Mideast influence.

Economic interests also play a role in Moscow's support for a nuclear deal, even if the lifting of sanctions trigged by an agreement would hurt Russia in the short run. These would put more Iranian oil on the market in competition with Russian crude.

But Moscow is reportedly working on a solution by offering cash for Iranian oil. Tehran then would spend the money on Russian goods. And Russia can sell the Islamic Republic state-of-the-art drilling equipment and other technology it needs to rebuild its sanctions-battered oil sector.

And in the long run, the Kremlin, which already helped construct Iran's working reactor, will benefit from an already signed multibillion-dollar deal to build two additional reactors and supply them with fuel. More such projects are planned, along with military cooperation and Russian arms sales to Tehran, including the long-delayed transfer of S-300 advanced air defense systems.

The U.S. has tried to desperately to prevent that system from reaching Iran.

The Iranians are clearly banking on Russia as they ready to shake off crippling economic sanctions. Tehran's ambassador to Moscow, Mehdi Sanayee, foresees a quick and "eye-catching leap" in bilateral trade with Russia from the present $5 billion a year to $70 billion.

And helping out on Iran may mean the U.S. and its partners ease their pressure over Ukraine.

"There may be a calculation by Moscow that the Western powers may be more reluctant to elevate sanctions over Ukraine in order not to jeopardize cooperation over Iran," Samore said.

By AP