Tedros Adhanom Ghebreyesus said he had spoken with Russian Foreign Minister Sergei Lavrov about the situation in Ukraine and Russia's role in global health matters.
"I requested safe access to Mariupol, Kherson, Southern Zaporizhzhia & other besieged areas to deliver health aid. Civilians must be protected," Tedros said on his Twitter feed.
Relations between the U.N. health agency and Russia have been strained since Russia launched its invasion of Ukraine on Feb. 24.
Members of the WHO's European region passed a resolution last week that could result in the closure of Russia's regional office and the suspension of meetings in the country.
The deputy speaker of the Russian lower house of parliament, Pyotr Tolstoy, submitted a list of Russia's agreements with international bodies, including the WHO, to the house earlier this week and proposed that the next step could be withdrawal, according to Interfax.
Moscow calls its actions in Ukraine a "special military operation" to disarm Ukraine and rid it of what it calls anti-Russian nationalism fomented by the West. Ukraine and the West say Russia launched an unprovoked war of aggression.
The WHO has reported some 235 attacks on health infrastructure in Ukraine since the conflict began, without attributing blame.
(Reporting by Emma Farge; Editing by Paul Carrel and Frances Kerry)
