LONDON (BLOOMBERG) - Vladimir Putin's annual economic forum in St Petersburg was always a hot ticket for Russian and foreign business tycoons eager to curry favour with the Kremlin by hosting glitzy parties or announcing major investments. His invasion of Ukraine has made it a radioactive one.

Many business leaders are concerned about even being seen at this year's St Petersburg International Economic Forum (Spief), fearful it may make them targets for sanctions, three sources familiar with the situation said, declining to be identified because the issue is sensitive.

At least two executives said they plan to leave early to avoid attending Mr Putin's speech at the event, which in past years was the highlight for the well-connected. Some have asked the organisers, Roscongress, not to identify them on their badges at the June 15-18 Spief forum, the people said. Roscongress did not respond to requests to comment.

Even as Russia contends with unprecedented international sanctions that threaten its deepest economic recession in decades, officials are projecting a business-as-usual approach for the 25th anniversary event under the slogan of "new opportunities in a new world".

The confrontation with the West that has escalated at times to warnings of nuclear war gets barely a mention on Spief's website, though foreign visitors are told to bring cash since sanctions mean Mastercard and Visa bank cards issued outside Russia will not work there.

Russia used previous forums to "demonstrate the success of the country" while business leaders could show they have "connections and money", said Ms Ekaterina Schulmann, a political scientist and fellow at Germany's Robert Bosch Academy, who moderated discussion panels at last year's SPIEF.

This year, "if domestic participants don't all want to demonstrate their participation, then foreign ones even more so," said Ms Schulmann, who has been labelled a "foreign agent" by the Kremlin.

Before the war, Russian tycoons and state-run companies competed to outdo each other by flying in entertainers like Sting and Robbie Williams, whose Party Like A Russian song caught the extravagant mood of Spief's late-night scene. Most of the same tycoons and companies are now under United States and European Union sanctions and few parties are planned this time.

Mr Putin's flagship event once attracted global political figures such as French President Emmanuel Macron, Chinese leader Xi Jinping and Indian Prime Minister Narendra Modi. This time, it is hosting an Afghan Taliban representative, according to the Tass news service, the investment minister from Myanmar's military government and the head of Venezuela's central bank, all heavily sanctioned countries.

Officials from Egypt, Turkey, the United Arab Emirates and the Central African Republic are also attending, as well as from former Soviet republics. Even so, the number of foreign representatives is a fraction of those at past Spiefs.

Despite their governments' sanctions on Russia, leaders of business organisations in Moscow representing France, Italy, Canada and the US are listed by Spief's organisers as taking part. An American Chamber of Commerce in Russia spokesman confirmed its participation.

Mr Putin did not mention what he calls Russia's "special military operation" in a greeting letter to participants that blamed "mistakes of Western countries" for surging global inflation, disruption to supply chains and food shortages.

But what he dubbed the "difficult time" in relations is reflected in much of Spief's program. Panels are dominated by Russian officials with few foreigners, and cover topics such as protecting "national media sovereignty" and boosting consumer and business patriotism in import substitution efforts.

Some previously prominent names at Spief are adopting a lower profile. Russia's largest lender, sanctioned state-run Sberbank PJSC, will not host its traditional party at the forum, two people familiar said.

Sanctioned billionaire Oleg Deripaska appeared to rule out his participation, saying the issue was "finally decided" in a June 8 Telegram post of cherry trees laden with fruit. "It's time to gather the harvest", said Mr Deripaska, who often spends time in his native agricultural Krasnodar region of southern Russia.

One programme highlight is Gazprom head Alexey Miller, a rare speaker at past forums, who will join a session on the global gas market, according to Spief.

The forum's high cost at 960,000 roubles (S$22,970) per person is causing some to skip the event because it makes less business sense with many international companies no longer in attendance, executives of two big industrial firms said.

"No senior executive of a foreign company will want to be photographed at SPIEF this year," said Mr Chris Weafer, chief executive of Macro-Advisory. Restrictions on travel to Russia are "a very convenient excuse for those that do not wish to attend and also do not want to burn bridges with the Kremlin".