Britain demanded answers from Russia yesterday after a couple was exposed to the same nerve agent used on a former Russian spy and his daughter in an attempted murder blamed on Moscow. But Russia quickly hit back, denouncing Britain for playing "dirty political games" and demanding London apologize.

The British couple fell ill on Saturday in Amesbury, a small town near the southwestern English city of Salisbury where former double agent Sergei Skripal and his daughter Yulia collapsed on March 4. That incident triggered a major diplomatic crisis with Russia after Britain and its allies accused Moscow of trying to kill them, a charge strongly denied by the Kremlin.

Speaking to parliament yesterday, Interior Minister Sajid Javid said a link between the cases was "clearly the main line of inquiry" and demanded Moscow explain itself.

"It is now time that the Russian state comes forward and explains exactly what has gone on," he said, noting the global focus on Russia as it hosts the football World Cup. "It is completely unacceptable for our people to be either deliberate or accidental targets, or for our streets, our parks, our towns to be dumping grounds for poison."

But his remarks sparked a sharp response from Moscow which suggested that the British police steer clear of involvement in political intrigues. "We urge British law enforcement not to get involved in dirty political games that certain powers in London have already begun and instead finally cooperate with Russian law enforcement in their investigations," foreign ministry spokeswoman Maria Zakharova told reporters. And the British government owed Russia an apology, she said. "This government and its representatives will have to apologize to Russia and the international community," she said, adding: "It will happen."