Russian Foreign Minister Sergey Lavrov was brought to the hospital upon his arrival in Bali for the Group of 20 meeting, Indonesian officials reported on Monday.
The Associated Press was told by three Indonesian government and medical officials that the Russian envoy was being treated on the resort island.
They all declined to be identified since they were not permitted to speak publicly about the situation.
According to two of the witnesses, Lavrov is being treated for a cardiac ailment.
The Russian Embassy could not be reached for comment immediately.
Earlier, amid the ongoing war with Ukraine, Russian President Putin had decided to skip the G20 summit, and if reports are to be believed, it is because he fears an assassination attemt.
Reports quoted Russian political strategist and Putin adviser Sergey Markov saying there is a big chance of assassination from the "from the special services of the U.S., Britain and Ukraine."
Rebekah Koffler, a former DIA intelligence officer had told Fox News there have over a dozen probable assassination bids on Putin throughout his tenure as a president. However, he also said that the speculation that the US or British intelligence would hatch a plot is "baseless and part of a "Russian disinformation".
G20 is the premier forum for international economic cooperation representing around 85% of the global GDP, over 75% of the global trade, and about two-thirds of the world population, it added.
Notably, G20 comprises Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, the Republic of Korea, Mexico, Russia, Saudi Arabia, South Africa, Turkey, the UK, the US and the European Union (EU).
(With Agencies Inputs)