The European Union is deciding what sanctions to impose on Belarus after President Alexander Lukashenko intercepted a Ryanair flight and detained Roman Protasevich, a dissident on board, and his girlfriend, Russian activist Sofia Sapega.

All 27 E.U. leaders agreed Monday to toughen sanctions on Lukashenko’s authoritarian government, bar E.U. airlines from traversing Belarusian airspace and prevent Belavia, Belarus’s national airline, from flying over or landing in E.U. territory. The Biden administration and U.K. officials have said they are weighing whether to follow suit.

On Friday, the White House announced that Washington will reimpose full sanctions against nine Belrusian state-owned enterprises. Biden administration officials are also coordinating with allies in the E.U. and elsewhere to develop “a list of targeted sanctions against key members” of Lukashenko’s regime, Press secretary Jen Psaki said.

During informal talks Thursday, E.U. foreign ministers floated sanctions on Belarus’s oil products and potash, a primary source of cash for the government, and German Foreign Minister Heiko Maas told reporters that more sanctions would probably follow in the absence of concessions.

But experts say it remains unclear how effective sanctions will be at influencing Lukashenko’s behavior.

Russian President Vladimir Putin met with Lukashenko on Friday. Russia, Belarus’s longtime economic and political lifeline, has stood firmly behind its ally, and analysts expect President Biden to press Putin on Belarus at their first face-to-face meeting next month. Putin and Lukashenko did not mention sanctions in their opening comments.

Economic sanctions — often posited as the best alternative to military force and a means of conveying liberal values — have become a favored tool in Washington and among many Western policymakers. They can consist of blanket prohibitions on trade with a country or restrictions on transactions with specific foreign entities or individuals. Since 9/11, international policymakers have generally favored the targeted approach.

The United States uses economic sanctions more than any other country. In recent months, the Biden administration has reinstated sanctions against Myanmar, targeted Russia over its imprisonment of an opposition leader and imposed sanctions on China for its actions in Hong Kong. The E.U. has levied sanctions several dozen times since the bloc’s establishment in 1992, according to the Council on Foreign Relations; without a joint military force, sanctions constitute the E.U.’s most potent weapon against foreign actors.

Dursun Peksen, a sanctions expert and political science professor at the University of Memphis, estimated that sanctions “fail at least 65 to 95 percent of the time.” He cited North Korea, which remains stubbornly totalitarian even though the Kim dynasty has been under U.S. sanctions for more than half a century, as a prominent example.

“Existing scholarship suggests that sanctions rarely work in achieving their intended policy objectives,” he said, but adding, “That doesn’t mean sanctions always fail.”

In general, experts say, sanctions are more effective at achieving their desired aims when they are multilateral, targeted and attached to specific, realistic goals. As an example of a “success” story, Peksen pointed to the Obama administration’s use of sanctions to get Iran to agree to negotiate the nuclear deal. The Trump administration’s barrage of sanctions aimed at regime change, on the other hand, served only to inflame tensions between Iran and the United States, he said.

In the case of Belarus, the E.U. and United States have both imposed several rounds of sanctions during Lukashenko’s nearly 27-year rule in response to his repressive practices. These include an E.U. arms embargo in 2004 after the disappearances of opposition politicians, a journalist and a businessman.

Europe dropped most of its sanctions in 2016 during a period of warmer relations with Belarus.

But after the 2020 presidential election in Belarus, which was widely seen as rigged in favor of Lukashenko and prompted mass protests that were heavily repressed, the E.U. placed additional sanctions on the Eastern European country. Eighty-eight individuals and seven entities are now subject to restrictions including travel bans and asset freezes.

The United States also issued fresh sanctions on Belarus. Since taking office, Biden has blocked transactions with nine major oil and petrochemical companies and placed sanctions on 109 officials.

The new E.U. slate will target critical sectors of the Belarusian economy, E.U. officials announced Monday.

Belarusian opposition groups are pushing the E.U. to ban companies from dealing with Belarus’s largest potash producer, a major fertilizer company, the oil group Belneftekhim and a number of refiners and banks, the Financial Times reported. They also proposed a moratorium on new foreign investment and credit links for Belarusian banks.

But such measures might not have a major effect on what is often described as the last Soviet-era economy. State-owned companies dominate the Belarusian economy, which is more dependent on Russia than on Western Europe or the United States.

Nearly half of all goods Belarus produces go to Russia, vs. about 24 percent to the E.U. And an arrangement with Russia that allows Belarus to import Russian crude oil, refine and resell it has accounted for a considerable portion of its gross domestic product.

“The most effective way to put pressure on Belarus is to find a way to cut Belarus’s close ties with Russia,” Peksen said.

Bruce Jentleson, a political science professor at Duke University, said flight restrictions are more likely than sectoral sanctions to significantly hurt Lukashenko and his circle.

Russia might be able to provide goods and machinery in lieu of the E.U., but “there’s no alternative partner” for E.U. airspace and airports, he said. “That’s where you have a sort of unique market control that is very difficult to substitute for.”

But sanction regimes also have a history of inflicting pain on civilians. In Syria, for instance, funding cuts to nongovernmental organizations as a result of sanctions have hindered the provision of humanitarian aid there.

“Lots of academic work on economic sanctions shows that they often misfire and hurt the groups you’re trying to help,” Jentleson said.

Belarusians will probably experience the adverse affects of additional sanctions. Some have already expressed fears that flight restrictions will block opponents of the government from fleeing the country.

Katsiaryna Shmatsina, a fellow at the Belarusian Institute for Strategic Studies, said that for many Belarusians, though, distress over mounting government repression will fuel support for the sanctions.

“The most proactive part of society that takes part in the protests, they stand for the sanctions, realizing that it puts more pressure on Lukashenko,” she said. “They are ready to suffer the short-term losses.”

Lukashenko hit back against the E.U. on Wednesday, calling sanctions and flight diversions a new kind of “hybrid attack” and predicting Russia would be the next target.

“I have to say that the events of the past few days attest to the increased, absolutely unfair pressure by Western countries on Belarus, which seems to be escalating,” Roman Golovchenko, Belarus’s prime minister, told Russian Prime Minister Mikhail Mishustin in Minsk on Thursday.

If Russia grows weary of providing financial support and of Lukashenko’s reticence to agree to a long-sought union, it is unclear how long Russia will continue coming to the rescue, experts said.

That was a wager Lukashenko was willing to make, Shmatsina said. With the international community and his own citizens casting his electoral victory as illegitimate — and the high likelihood that he would be prosecuted if a more democratic leader took over — he will do whatever it takes to hold on to power, she said, even if it risks international opprobrium.

“The Lukashenko regime is in survival mode,” Shmatsina said. “They have no exit scenarios.”