Washington(CNN) Secretary of State Mike Pompeo sent a cable to all US missions overseas ordering diplomats not to meet with Iranian opposition groups without specific approval because it could further exacerbate tensions with the Iranian regime.

"Many exiled Iranian opposition groups try to engage U.S. officials regularly to gain at least the appearance of tacit support and enhance their visibility and clout," Pompeo said, according to a copy of the cable obtained by CNN. He noted that many of these groups "have previously or are currently using violent means in support of their political aims."

"Direct U.S. government engagement with these groups could prove counterproductive to our policy goal of seeking a comprehensive deal with the Iranian regime that addresses its destabilizing behavior," Pompeo wrote.

The cable's existence, first reported by Bloomberg, is coming to light in the aftermath of the deadly US drone strike that President Donald Trump ordered last week to kill Iranian Gen. Qasem Soleimani.

Pompeo sent the instructions early this week and his indirect reference to attempts at diplomatic outreach to Iran comes as the Trump administration has refused to issue a visa to Iran's top diplomat, Foreign Minister Mohammad Javad Zarif.

In recent days, Trump administration officials have not laid out any specific steps they are taking to engage in diplomacy with Iran, though they have said they are willing to do so. Iran, over the last year, has not acted upon any of Trump's comments that he is willing to meet Iranian leadership, but Zarif said publicly he was willing to discuss prisoner exchanges.

The cable lists a number of Iranian opposition groups, including Mujahedeen-e-Khalq, known as the MEK, and five other Iranian opposition groups that are off limits without specific approval. John Bolton, Trump's former national security adviser, has previously said the MEK is a "viable opposition" to the current Iranian regime.

Last month Rudy Giuliani, Trump's personal attorney, met with Iranian opposition groups that are linked to the MEK. Bolton and Giuliani have also given paid speeches on the group's behalf. During one of those speeches last year, Giuliani called for regime change in Iran.

The MEK, which was previously on a US terrorism list, paid Bolton to give speeches on its behalf and once employed Giulianir.

Pompeo warned in the cable that it would be "counterproductive" to engage these groups. He said some of them have histories of using violence to achieve political objectives and that some of them seek to overthrow the Iranian regime.

Given the escalating tensions with Iran in the wake of the strike on Soleimani, the cable appears to be an attempt to demonstrate that the Trump administration wants to avoid the perception that it is conspiring with opposition groups to push for regime change.

In the cable, Pompeo cited the administration's willingness to seek a "comprehensive deal" with Iran that covers a range of Iranian activities including "its destabilizing behavior, including its nuclear program, missile program, support for terrorism, and malign regional behavior."

The State Department has not replied to a request for comment on the cable.

It's not clear which Iranian officials the US administration would engage. In an NPR interview aired Tuesday, Zarif said he had requested the visa 25 days ago but the US State Department told him it "didn't have enough time to issue a visa."

In an interview with CNN's Fred Pleitgen, Zarif said he wasn't concerned about the Trump administration barring him entry to the US. When asked about his reaction to being denied the visa, Zarif answered with a laugh, "Well, what are they afraid of?"

Pompeo, speaking at the State Department on Tuesday, said that "we don't comment on visa matters for those traveling to the United States," and added that "we will always comply with our obligations" under the UN charter.

US officials are not completely disengaging with groups who oppose the Iranian regime. On Tuesday Brian Hook, the State Department special representative for Iran, met with leadership from the Simon Wiesenthal Center leadership, a Jewish human rights organization.

Members of the center praised the Trump administration for the Soleimani strike and one of them urged additional killings of Iranian leaders.

"The entire leadership of Iran denies the existence of the Holocaust and we have to worry about how we treat them. If they are going to kill American soldiers, we have an obligation to do what President Obama did to Osama bin Laden, what the President of Czechoslovakia did to Reinhard Heydrich, that should be done to the Iranian leaders," Rabbi Marvin Hier, the founder of the center, said on Tuesday.