Russia's Chief of General Staff Valery Gerasimov and US Joint Chiefs of Staff Chairman General Mark Milley held a phone call, RIA news agency reported on Thursday, citing the Russian defense ministry.
They discussed issues of "mutual interest," including Ukraine, RIA said.
The call took place six days after a phone conversation between the defense ministers of the two countries, their first since Russia launched what it calls its special military operation in Ukraine.
Russia's siege of the Ukrainian city of Mariupol stuttered towards its end on Thursday, with hundreds of fighters still holed up in the catacombs of the Azovstal steelworks and some 1,700 who have already surrendered and face an uncertain fate.
A full abandonment of the bunkers and tunnels of the bombed-out plant would end the most destructive siege of a war that began when President Vladimir Putin ordered the invasion of Ukraine on February 24.
But it was unclear how many fighters remained inside. Russia's defense ministry said 771 fighters from the Azov Regiment — vilified by Russia — had surrendered in the past day, bringing the total of those who had given themselves up since Monday to 1,730. Ukrainian officials, however, declined to comment, saying it could endanger rescue efforts.
Denis Pushilin, head of the Russian-backed separatist Donetsk People’s Republic, which now encompasses Mariupol, said more than half the Ukrainian fighters had surrendered, and that the uninjured had been taken to a penal colony at Olenivka, near Russian-controlled Donetsk.
"Let them surrender, let them live, let them honestly face the charges for all their crimes," he told the Solovyov Live online video channel.
Russia needs the city, one of Ukraine's main seaports, to cement its control of the swathe of land it has seized along Ukraine's coast, reaching all the way west to annex Crimea.
But the city is now an urban wasteland shattered by artillery and street-by-street fighting. Before the war, its population was around 430,000. Pushilin said approximately 200,000 remained, although Ukrainian officials have said it is only half that number.
Military, economic aid for Ukraine
The Group of Seven (G7) industrialized nations have committed $18.4 billion in transfers and loans to help Ukraine meet its immediate financing needs, according to a draft communique seen by Reuters on Thursday.
"We have mobilized 18.4 billion US dollars of budget support, including 9.2 billion US dollars of recent commitments in the lead up to the Petersberg meeting, to help Ukraine close its financing gap and continue ensuring the delivery of basic services to the Ukrainian people," the G7 finance ministers and central bankers said in the draft document.
US President Joe Biden could sign off on $100 million of military aid to Ukraine as soon as Thursday, including additional artillery munitions and counter artillery battery radars, the latest in a series of transfers to help Kyiv repel Russia's invasion, according to two sources briefed on the matter.
A Ukrainian general said on Thursday the evacuation of Ukrainian troops from the city of Mariupol was continuing but provided no details.
"In the Mariupol direction, measures are being taken to evacuate our heroes," Oleksiy Gromov, Deputy Chief of the Main Operational Department of the General Staff of Ukraine's Armed Forces, told an online briefing.
Moscow said on Thursday that 1,730 Ukrainian fighters had surrendered in Mariupol over three days, including 771 in the past 24 hours.
WHO asks for medical access
The head of the World Health Organization has urged Russia to ensure safe access to places in Ukraine that its troops control or are besieging, to allow healthcare to be delivered to people.
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 UN health agency and Russia have been strained since Russia launched its invasion of Ukraine on February 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.
Clashes in Luhansk
12 Ukrainians were killed and over 40 were wounded by Russian shelling in Severodonetsk, in the Luhansk region, on Thursday, Luhansk Regional Military Administration Serhiy Haidai said.
The shelling, which was directed at residential buildings, according to Haidai, is "continuing even now."
"Data on the dead and injured are still being clarified, as it is impossible to inspect the area under fire," he added.
China to buy Russian oil?
China is in talks with Russia to buy additional supplies of oil in order to add to its strategic crude inventories, according to a Bloomberg News report on Thursday.
The crude would be used to fill China's strategic petroleum reserves, and talks are being conducted at a government level with little direct involvement from oil companies, Bloomberg reported, citing one person with knowledge of the plan.
The United States banned imports of Russian oil shortly after Moscow's invasion, while the European Union is considering a phased embargo, pushing more Russian oil cargoes towards Asia.