The world body is also rallying the international community to provide speedy assistance that can help save lives and put people on the road to recovery, a UN spokesman said at a daily news briefing held here on Monday, Xinhua reported.
The floods in Serbia, Bosnia-Herzegovina and Croatia have caused the deaths of 36 people and forced tens of thousands to be evacuated.
UN Emergency Relief Coordinator Valerie Amos said that she was concerned by the impact on people, many of whom remained without electricity or clean water and face health problems, according to UN spokesman Stephane Dujarric.
"The UN Office for the Coordination of Humanitarian Affairs ( OCHA) has dispatched a UN Disaster Coordination and Assessment team to Serbia and life-saving supplies are on their way from Brindisi," Dujarric said.
"Our humanitarian colleagues says that the rains have eased and water levels of most rivers are slowly reducing -- except for the river Sava which continues to pose a threat -- but many areas are still physically cut off and only reachable by helicopter or boat, " Dujarric said.
Teams from the World Food Programme (WFP), the UN Refugee Agency (UNHCR), the UN Children's Fund (UNICEF), the UN Development Programme (UNDP) and the International Organization for Migration are working with the authorities to help assess people's needs and provide food, clean water and sanitation support and debris removal, he said.
"In all three countries, the government is leading the flood response, distributing food and other relief supplies, and providing emergency shelter," the spokesman said. "The United Nations and humanitarian partners have offered assistance to the authorities."
The World Food Programme (WFP) on Monday sent a second batch of emergency relief items to Serbia. The first charter flight arrived in Belgrade, capital of Serbia, last night, according to the spokesman.