At least 1 lakh people have likely been displaced by violence amid reported missile attacks from Russia's "special military operation" in Ukraine, including the capital Kiev and other cities, the UN said Friday.

Forced mass displacement has also begun, the UN refugee agency (UNHCR) confirmed.  

"There are more than 100,000 who we estimate have lost their homes and are displaced inside [the] country and we are also aware of several thousand who have crossed international borders in the region, and we've seen those really just happening since the onset of the situation," said UNHCR spokesperson Shabia Mantoo. 

"We're seeing these reports and we've seen for instance yesterday that there were about 5,000 refugee arrivals in Moldova already, but the other movements are being reported in Poland, Romania, Slovakia and the Russian Federation."

Read: Ukraine invasion: What to know as Russian forces target Kyiv

"There have been major attacks in Kiev that have created greater fear and panic among the population, with families really scared, moving alongside their children into subways and shelters," said Afshan Khan, UN Children's Fund (Unicef) Regional Director, Europe and Central Asia. 

UN Secretary-General António Guterres Thursday appealed for peace and allocated $20 million from the Central Emergency Response Fund (CERF) to meet urgent needs. 

The use of force by one country against another is "the repudiation of the principles that every country has committed to uphold," which applied to the military offensive in Ukraine, Guterres said.  

Civilian deaths confirmed 

Two days since Russia launched military operations inside Ukraine, the UN rights office, OHCHR, confirmed that well over 100 civilians have already been killed. 

"We've received reports of at least 127 civilian casualties; this includes 25 killed and 102 injured in Ukraine, caused by shelling and airstrikes…this is very likely to be an underestimate," said Ravina Shamdasani, OHCHR spokesperson. 

Communities are already in need of aid relief, too, UN humanitarians said. 

Fuel, cash, medical supply shortages 

"When we look at shortages, we're talking about fuel, which has been well reported in the media, we're talking about cash, because often in humanitarian situations, cash assistance would be our first support to families, so obviously there's been a drawdown on banks," said Unicef's Afshan. 

In an appeal for guaranteed humanitarian access to the most vulnerable individuals, the World Health Organization (WHO) highlighted concerns that medical teams faced being overwhelmed. 

"We don't have reports yet from the hospitals when we look to particular injuries and the details of medical," said Jarno Habicht, WHO Representative in Ukraine. "Where our focus has been now, is that the prepositioned medical kits. We will run out of them soon, so what is important currently...is how to ensure new supplies to come and...[that] there are humanitarian corridors from the neighbouring countries available."  

The UN agencies have been active in Ukraine for many years, particularly since Russia's annexation of Crimea in 2014 – a move in large part rejected by the international community.