Overall, 68% say ISIS is a very serious threat, compared with just 39% who say so about Iran, 32% about North Korea, 25% on Russia and 18% on China. Nearly 9 in 10 see ISIS as at least a moderately serious threat.

The partisan divides that often drive public opinion around foreign policy issues are less prominent when Americans rate the threat from ISIS. Majorities across political and ideological lines say ISIS is a deeply serious threat to the U.S., including 68% of Democrats, 79% of Republicans and 63% of independents.

With active fighting against the Islamic State militant group in Iraq and the arrests Sunday of six Minneapolis men accused of trying to join ISIS, concerns about the threat posed by the group grow alongside worries that the military battle could spread. While a CNN/ORC Poll in March found the public remained mostly confident that the U.S. effort to combat ISIS would succeed, it also showed 79% of Americans were worried that the conflict would develop into a larger war that would spread throughout the region and to other parts of the world.

The party unity in perceptions of ISIS as a threat do not extend to Iran, however, with the new CNN/ORC poll showing a broad partisan rift in perceptions of Iran's threat to the U.S. According to the poll, Republicans are far more apt to see Iran as a very serious threat than Democrats or independents (53% of Republicans call it a very serious threat compared with 38% of independents and 29% of Democrats).

That partisan divide carries through to perceptions of an agreement in the works between the U.S. and Iran that would lift some economic sanctions in exchange for greater access to and limitations on Iran's nuclear program. If Iran were to violate the terms of such an agreement, however, majorities in both parties say military action should be the next step.

The CNN/ORC poll finds 53% favor the U.S. and Iran making an agreement that would ease some economic sanctions in exchange for major restrictions on Iran's nuclear program alongside greater international inspection of Iran's nuclear facilities, 43% say they oppose such an agreement. Democrats broadly back the deal (67% favor it), Republicans largely oppose it (60% opposed). Support for the deal is strongest among liberals (69% favor it) those under age 35 (63%) and those who have attended college (60%).

The more likely a person is to see Iran as a threat to the United States, though, the less likely they are to back the deal. Among the 39% who see Iran as a very serious threat, a majority (56%) oppose the deal. Among the 27% who see Iran as a slight threat or no threat at all, two-thirds favor the deal (66%), while just 28% oppose it.

The U.S. and other countries reached a preliminary framework with Iran for such a deal earlier this month, but talks continue toward a final agreement, with a June 30 deadline. Congress and the White House reached agreement on a bill last week that would allow Congress to review any deal reached with Iran before certain economic sanctions can be lifted.

If an agreement is reached and put into place and Iran violated its terms, most Americans feel a military response is in order. The poll finds 61% say the U.S. should take military action if Iran broke the agreement. Across the board, majorities of Americans support military action if Iran were to violate the terms of the deal: Republicans (67%), independents (60%) and Democrats (58%) all break in favor of taking military action in that instance. Support for military action drops below 50% among liberals, but just barely (49% say the U.S. should take military action if the terms are violated, 48% that it should not).

Support for military action is higher among those who oppose any deal to begin with. Among that group, 70% say the U.S. should take military action if Iran violates the terms of the agreement. A majority of those in favor of the deal back military action in response to a violation of terms, but it's a smaller majority at 55%.

Overall, Americans are divided on how the President is handling the U.S. relationship with Iran, 48% approve while 48% disapprove. Opinions of the president's handling of Iran are divided by party, with 79% of Democrats approving while 77% of Republicans disapprove. But Obama's handling of Iran earns him higher marks among Republicans (19% approve) than his overall handling of the presidency (11%). At the same time, Democrats are less apt to approve of Obama's Iran policies (79%) than of his handling of the presidency more broadly (88%).

The CNN/ORC International poll was conducted by telephone April 16-19 among a random national sample of 1,018 adults. Results for the full sample have a margin of sampling error of plus or minus 3 percentage points.