Sir Karl, 91, says that the Balkan states should be given an ultimatum that air forces would destroy any military installations if the fighting did not stop immediately.
He said: 'Since the civil war is over and since this is now a war of aggression of state against state, we are committed under the existing treaties to interfere. If we do not, we are violating our most important duties.'
Sir Karl's intervention is significant because of the influence he exerts on politicians, most famously through The Open Society and its Enemies, an argument for political democracy written during the Second World War.
The book, which blamed Plato for the rise of Hitler, is only now being published legally in Russia because of the vehemence of its anti-Marxist views.
Baroness Thatcher has always included herself among 'Popperian' disciples, although he refuses to be pigeon-holed. He said last year that he had been a socialist for several years, even after his rejection of Marxism, 'and if there could be such a thing as socialism combined with individual liberty, I would be a socialist still'.
Born in Vienna, he became a naturalised British citizen in 1945, and was professor of logic and scientific method at the London School of Economics from 1949 to 1969. He took apart the linguistic theories of Wittgenstein, who had dominated post-war English philosophy.
Sir Karl remembers a seminar at which he was discussing the validity of moral rules. Wittgenstein, sitting near a fire, jumped up, brandishing the poker. 'Give me an example of a moral rule,' he shouted, to which Popper replied: 'Not to threaten visiting lecturers with pokers.'
In 1957, Sir Karl produced his most controversial work, The Poverty of Historicism, another attack on Marxism, which led to him being described as a reactionary. Sir Karl countered with 'criticism of my alleged views was widespread and highly successful. I have yet to meet a criticism of my views.' Sir Karl's statement, passed to the Independent, says:
'We Europeans demand immediate action to stop the murder in the former Yugoslavia.
'It has to be stopped now, because the murder is going on now. It has to be stopped because of the future of mankind, not only of Europe. Only a determined show of force can stop it.
'Ground-fighting in Yugoslavia must be avoided (Vietnam]), even though ground forces must be made available. The operations must be from the air, and the forces to be collected as quickly as possible must be overwhelming. An ultimatum must be issued that the fighting has to stop at once, otherwise our air force will destroy any military installations: tanks, aeroplanes, airfields.
'An organisation must be built up to enable us to repeat this show of strength again, if necessary, within a day (if, as is to be hoped, the first show of strength leads to a cessation of military operations). The continued threat of military intervention must be maintained as long as it is necessary.
'Of course, humanitarian help from the air has to be continued. If some of the parcels that are dropped fall into the wrong hands, it does not matter much; on the contrary: all the soldiers are human beings who are victims of their government. Since the civil war is over and since this is now a war of aggression of state against state, we are committed under the existing treaties to interfere.
'If we do not, we are violating our most important duties.'Reuse content