WASHINGTON — The Obama administration said Thursday that a proposed Russian sale of fighter jets to Iran would violate a U.N. arms embargo on Tehran, setting up another standoff related to last year's nuclear negotiations.

State Department spokesman Mark Toner said transferring the Sukhoi-30 jets, comparable to American F-15E fighter bombers, requires the U.N. Security Council's approval.

The U.S will raise the matter with Russia, Toner said, adding that all six countries that negotiated July's landmark nuclear agreement with Iran "should be fully aware of these restrictions." The deal kept the arms ban on Iran in place for up to another five years.

Iran's defense minister said last week that the Islamic Republic would purchase an unspecified number of the Russian planes. Gen. Hossein Dehghan provided no timeline for delivery, but said Iran would be involved in producing the aircraft.

The dispute is the latest linked to the nuclear negotiations that ended last July in a deal setting long-term limits on Iran's uranium and plutonium programs in exchange for hundreds of billions of dollars in future sanctions relief.

The U.S. and its negotiating partners — Britain, China, France, Germany and Russia — reached an understanding with Iran to phase out U.N. bans on Iranian weapons deals and ballistic missiles work after periods of good behavior.

Both embargoes are still in effect, though U.S. officials say Iran has conducted at least two ballistic missile tests since last summer. In response, Washington imposed new sanctions on Iran just hours after five American citizens left Iran as part of a prisoner exchange last month.

Like the ballistic missiles work, U.S. officials say the Russian plane sale wouldn't constitute a nuclear deal breach. But it would amount to another in a long string of Iranian transgressions of U.N. Security Council resolutions.

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Toner said the Sukhoi qualifies as "combat aircraft" under the U.N. register of conventional arms. Sales of these to Iran require the Security Council's approval "in advance on a case-by-case basis," he said.

Iran regained access to tens of billions of dollars in frozen assets overseas when it satisfied its obligations under the nuclear deal last month.

Iran's rivals in the Middle East are worried by the windfall. Shiite Iran is battling the Saudi Arabia and other Sunni countries in proxy conflicts in Syria and Yemen, and Israel is threatened by Tehran's support for militant groups Hamas and Hezbollah.

Dehghan said Iran would seriously focus on its "air force and fighters," a fleet the still heavily depends on domestically modified versions of long-outdated warplanes, including former Soviet MiGs and American F14A Tomcats from the 1970s.

The U.S. also is concerned by Russia's delivery of advanced S-300 air defense missile systems to Iran. That deal was frozen in 2010, but Russian President Vladimir Putin approved its transfer last April. Unlike the fighter jets, however, the S-300 is defensive and not covered by any U.N. prohibition.