KYIV, Ukraine (NewsNation) — The United Nations and its partners have been delivering supplies for thousands of people in Ukraine’s northeast region, but they have been unable to reach some in southern cities, the organization’s humanitarian coordinator said Thursday.

Even though the U.N.-facilitated humanitarian notification system with Ukraine and Russia allowed the convoy of supplies to get to Sumy, efforts to reach besieged Mariupol, Kherson and other encircled cities in the south have been unsuccessful because of safety concerns.

Food rations from the humanitarian organization People in Need and the U.N. World Food Program will benefit nearly 6,000 people in Sumy and areas such as Trostianets and Okhtyrka. Basic household items including blankets and kettles from the U.N. refugee agency will support 1,500 people, while sanitation kits will help 6,000 people with hygiene and drinking water.

Six weeks into the Russian invasion of Ukraine, which has left thousands dead, the number of Ukrainians fleeing the country topped a staggering 4 million, half of them children, according to the United Nations.

Russian President Vladimir Putin announced Thursday he is adding 134,500 new troops to the Russian army in its spring draft.

Sergei Shoigu, Russia’s defense minister, said new recruits will not be sent to “hot spots.”

Also Thursday, Russian troops are leaving the Chernobyl nuclear power plant, heading toward the Belarus border after soldiers got “significant doses” of radiation from digging trenches at the highly contaminated site, Ukraine’s state power company said.

Energoatom, the operator, gave no immediate details on the condition of the troops or how many were affected. But it said the Russians had dug in in the forest inside the exclusion zone around the now-closed plant, the site in 1986 of the world’s worst nuclear disaster.

Despite Russia’s reneging on a pledge to scale back some of its operations, Ukrainian President Volodymyr Zelenskyy said his country’s defense against the Russian invasion was at a “turning point.”

Zelenskyy asked the United States and its allies for more help as Russian shelling of areas around Kyiv and the northern city of Chernihiv intensified, further undermining hopes for progress toward ending the monthslong conflict. 

“If we really are fighting for freedom and in defense of democracy together, then we have a right to demand help in this difficult turning point. Tanks, aircraft, artillery systems. Freedom should be armed no worse than tyranny,” Zelenskyy said in his nightly video address, which he delivered standing in the dark outside the dimly lit presidential offices in Kyiv. He thanked the U.S. for an additional $500 million in aid that was announced Wednesday.

Russian troops also stepped up their attacks on the Donbas region in the east and around the city of Izyum, which lies on a key route to the Donbas, after redeploying units from other areas, the Ukrainian side said.

Russian and Ukraine officials said Thursday they would attempt another evacuation from the hard-hit city of Mariupol.

Tens of thousands have managed to get out in the past few weeks by way of humanitarian corridors, reducing the city’s population from a prewar 430,000 to an estimated 100,000 as of last week, but other efforts have been stalled by continued Russian attacks.

Zelenskyy said the continuing negotiations with Russia were only “words without specifics.” He said Ukraine was preparing for concentrated new strikes on the Donbas.

Oleksandr Pavliuk, head of the Kyiv region military administration, said Russian shells targeted residential areas and civilian infrastructure in the Bucha, Brovary and Vyshhorod regions around the capital.

Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said the military also targeted fuel depots in two towns in central Ukraine with air-launched long-range cruise missiles. Russian forces hit a Ukrainian special forces headquarters in the southern Mykolaiv region, he said, and two ammunition depots in the Donetsk region, in the Donbas.

In southern Ukraine, a Russian missile destroyed a fuel depot in Dnipro, the country’s fourth-largest city, regional officials said.

The U.S. said Russia had begun to reposition less than 20% of its troops that had been arrayed around Kyiv. Pentagon press secretary John Kirby said troops from there and some other zones began moving mostly to the north, and some went into neighboring Belarus. Kirby said it appeared Russia planned to resupply them and send them back into Ukraine, but it is not clear where.

Russia is also expected to try to blockade Chernihiv.

The Russian military said it committed to a localized cease-fire along the route from Mariupol to the Ukrainian-held city of Zaporizhzhia Thursday morning.

Peace talks between Ukraine and Russia are set to resume Friday by video. The U.N. nuclear watchdog said Thursday its director-general arrived in Russia’s Baltic Sea exclave of Kaliningrad for talks with senior Russian officials.