There are confirmed cases of bird flu in dairy cattle in eight US states, according to the US Department of Agriculture
The fighting killed at least seven people and forced a halt to all flights in the worst violence in the capital in six months.
"We can confirm a temporary relocation for security reasons," UN spokesman Farhan Haq said, without giving figures.
If the security situation continued to deteriorate, UN sources did not rule out a temporary relocation of all remaining international staff in Libya. One UN source said UN staff had been "significantly reduced."
The United Nations Support Mission in Libya, or UNSMIL, has some 200 national and international staff, according to its website.