The expulsion of Russia from a major global financial system will cast a shadow over the world economy, which has already been hurt by the COVID-19 pandemic, experts said.

The United States, the United Kingdom, Canada and the European Union said in a joint statement on Saturday that "selected Russian banks" will be removed from the SWIFT messaging system, which stands for the Society for Worldwide Interbank Financial Telecommunication.

These affected Russian banks, about which additional details were not disclosed, will be "disconnected from the international financial system", according to the statement.

Belgium-based SWIFT, founded in 1973, is a secure messaging system used to facilitate cross-border money transfers, instead of taking part in payments directly. It connects more than 11,000 banks and financial institutions in more than 200 countries. It processed 42 million financial messages each day in 2021, up 11.4 percent year-on-year.

A comment piece in May last year from the Carnegie Moscow Center think tank described expulsion from SWIFT as a "nuclear option" that would hit Russia particularly hard, primarily because of the country's reliance on energy exports denominated in US dollars.

"The cutoff would terminate all international transactions, trigger currency volatility, and cause massive capital outflows," according to the article's author, Maria Shagina.

Yang Xiyu, a researcher at the China Institute of International Studies, said that excluding Russia from SWIFT will bring harm to all related parties, including in the US and Europe. Such a stalemate, if it lasts longer, would seriously impair the world economy, Yang said.

Tan Yaling, head of the China Forex Investment Research Institute, also agreed that the US and Europe will undergo much pressure by cutting off Russia from SWIFT, as Russia is a major food and energy exporter in the world. The expulsion might be short-term, as trade suspension would result in two-way negative impact in the globalized market.

The EU is the world's largest natural gas importer, with 41 percent of the annual imported volume coming from Russia, according to the energy department of the European Commission.

The stress on "selected banks", instead of the entire Russian banking system, leaves room for the EU so that it can continue US dollar-denominated natural gas imports from Russia, said Dong Ximiao, chief researcher at Merchants Union Consumer Finance.

More than 95 percent of the world's cross-border US dollar-denominated transactions are processed by combining the services from SWIFT and the New York-based Clearing House Interbank Payment System, according to experts at Guotai Jun'an Securities.

Hong Hao, managing director of BOCOM International, said that Russia and most of the European economies will have to avoid US dollar payments if they wish to continue natural gas trade after such an expulsion takes effect, which eventually would rattle the US dollar's dominating position in the world.

SWIFT cut its connection with Iran in 2012 and 2018, and a similar step was taken against the Democratic People's Republic of Korea in 2017.

Tan from the China Forex Investment Research Institute emphasized that the steps taken against Iran and the DPRK were completely different from the expulsion of Russia, given the latter's economic size and global influence. In addition, the world economy was different in the earlier cases, since the measures were taken before the impact of the pandemic, Tan said.

Zhou Lanxu in Beijing contributed to this story.