NATO spokesman Jamie Shea told a news conference that the reports from a variety of sources indicated that "dark things are happening" in Kosovo, although their extent was not yet completely clear.
The rebel Kosovo Liberation Army's press agency said fighting continued throughout the province Friday, with reports that Serbs killed more than 30 in "mass executions," including 20 slain in Orahovac and 10 in Podujevo.
Serbian officials, meanwhile, said the KLA had stepped up attacks on Serb forces in the province.
More than 2,000 pro-Serb demonstrators stormed a hotel in Macedonia Friday, which houses staff from NATO and Western media, reports CBS News Correspondent Randall Pinkston.
As reporters scrambled to get out of the way, the mob let loose with rocks and firebombs. Police moved in, making some arrests, but mostly trying to contain the protesters.
Embassy buildings belonging to the U.S., England and Germany were also targets of attacks in Moscow, where the diplomatic compound was pelted with eggs and ink.
As a result of the protests, the State Department advised American embassy workers in Macedonia to leave.
Press Secretary Joe Lockhart said Friday that President Clinton is "determined" to see the NATO action through to its completion and achievement of its objectives.