LONDON (Reuters) - British Defence Secretary George Robertson warned on Friday that NATO was ready to bomb Yugoslavia "night after night" as another wave of U.S. B-52 bombers took off from a British air base. Robertson said there would be no let-up as long as Yugoslav President Slobodan Milosevic continued what he said were genocidal attacks on ethnic Albanians in Kosovo. "If he (Milosevic) keeps on with the killing, then night after night we will take more and more chunks out of his murder machine," Robertson told BBC television. A short time later four U.S. B-52 bombers, massive warplanes which were involved in Wednesday‘s first day of air strikes against Yugoslavia, took off from a Royal Air Force base at Fairford in western England. The bombers were loaded with cruise missiles, witnesses said. Yugoslav ambassador Milos Radulovic grimly watched live television pictures of the bombers taking off. "We are really very angry, and we have good cause to be angry, because this is…aggression on a sovereign state, a state which holds more than 700,000 refugees," he said. Radulovic spoke as he and other Yugoslav envoys in Britain packed to leave the country after Belgrade cut diplomatic ties with Britain and other NATO countries. Prime Minister Tony Blair will make a televised address about Yugoslavia at 6 p.m. (1800 GMT), Downing Street said. In several interviews with British media, Robertson denounced as genocidal the Yugoslav army‘s "savage, inhuman, brutal, merciless attacks" on the ethnic Albanians of Kosovo. Robertson said NATO, which pounded Yugoslavia with missiles and bombs for a second night, had never promised its air strikes against Yugoslavia would be a one-day campaign. But he insisted the strikes were already damaging Milosevic‘s ability to carry out assaults on Kosovo. "We never said there was going to be some overnight knockout blow," Robertson said. "But we are damaging his capability. We are affecting his morale. We are affecting the way in which the destruction of villages has taken place, the genocidal attacks on the Kosovo people have taken place." Robertson said Milosevic was trying to systematically wipe out ethnic Albanians in Kosovo, "using a sort of savagery that hasn‘t been seen in Europe since the Middle Ages". "It‘s time for President Milosevic to stop the killing and to start the talking again, and at any point he can do it," Robertson said. "The next step is up to him." Asked by BBC radio about statements by Greek officials that the NATO attacks might not be a solution, Robertson denied there were major disagreements over the NATO strategy. He said no one had suggested any alternative to NATO‘s current action that would stop ethnic cleansing in Kosovo. "Greece may be expressing a degree of nuance," he said. "They said they weren‘t going to get involved… but they have given very substantial logistical help." As for Russian protests: "The Russian position is perfectly understood, but they were party to the demands made of President Milosevic (to stop attacks on Kosovo) and they haven‘t yet suggested an alternative (to NATO action)," he said.