MOSCOW — Britain’s confrontation with Russia escalated yesterday when the Kremlin ordered the tit-for-tat expulsion of four British diplomats from Moscow. David Miliband, the foreign secretary, denounced this response to Britain’s ejection of four Russian diplomats as “completely unjustified.”

He repeated his call for Moscow to hand over Andrei Lugovoi, the main suspect in the murder of the former KGB spy, Alexander Litvinenko, in London last year.

Russia’s move came as Mr. Miliband delivered his first speech since taking over at the Foreign Office. In a lecture at Chatham House, London, he said that Britain should be a “global hub” and place combating “extremism, radicalization, and conflict” as the first priority of its foreign policy.

Russia, however, remains defiant against British pressure and says that its constitution prevents Mr. Lugovoi’s extradition.

“Four British embassy staff are persona non grata and should leave the Russian Federation within 10 days,” Mikhail Kamynin, the Foreign Ministry spokesman, said. Anthony Brenton, the British ambassador, was summoned by the Russian foreign ministry and handed the names of those to be expelled. Their identities were not released.

Russia also imposed a visa ban on British officials and said it would cease cooperation with London in the war on terrorism. Robust though Moscow’s response was, it came at the lower end of the spectrum of possible retaliation. There were fears that the Kremlin would eject a greater number of British diplomats — which could have forced Britain into taking additional steps.

“We kept our nerve and were right to do so,” a Whitehall source said. “It doesn’t look like we’ll have to do more in terms of further expulsions.”

In a significant diplomatic victory, Mr. Miliband has won the backing of America and the European Union — leaving Russia looking isolated.

Secretary of State Rice and Bernard Kouchner, the French foreign minister, both called their Russian counterpart, Sergei Lavrov, to express concerns about Russia’s behavior.

Miss Rice told Sky News Russia should meet the request for Mr. Lugovoi’s extradition.

“A terrible crime has been committed on British soil,” she said. “Russia should honor the extradition request and cooperate fully.” There have been signals that the Kremlin is keen to repair ties with Britain — at least in part. Yesterday, President Putin referred to a “mini-crisis” in Anglo-Russian relations and said it could be overcome.

“A response exceeding London’s tough steps was not discussed,” said Alexei Gromyko, the director of the British Studies Center, an official think tank with close ties to Russia’s Foreign Ministry. “By not retaliating with tougher measures, Moscow is sending a signal that normalization of relations is now in London’s hands.”

In his speech, Mr. Miliband said: “Just as the city of London acts as the center of the global financial market, British cities and institutions and ideas can become the hubs for scientific, cultural, and political collaboration.”

Mr. Miliband said America would continue to be Britain’s “single most important” ally and that Prime Minister Brown’s government would be willing to use military force where necessary. There was a “continued role for hard power intervention,” he said.

The foreign secretary cited the war in Kosovo in 1999 as an example of successful military action designed to stop “ethnic cleansing.”