Gordon Brown announced three new cases of swine flu in Britain today as a US official confirmed the first death outside Mexico from the new H1N1 flu strain.

The Prime Minister told MPs that a 12-year-old girl from Torbay, in Devon, was among the confirmed cases. Two adults have also contracted the virus, one from London and one from Birmingham.

"All have recently returned from Mexico, all have mild symptoms and all have responded well to treatment ... with Tamiflu," Mr Brown added.

He said that the girl's school in Torbay had been closed and pupils there were being treated with anti-viral drugs. "The World Health Organisation has said that we are one of the best prepared countries," Mr Brown told the Commons. "We intend to keep it that way."

The Prime Minister was speaking shortly after news emerged of the death of a 23-month-old child in Texas, one of 112 confirmed cases in the United States, most of which have been considered mild.

Dr Richard Besser, acting director of the Centres for Disease Control, told CNN: "I can confirm the very sad news out of Texas that a child has died of the H1N1 virus."

Mexican officials say that 159 people have died there of the virus, although the World Health Organisation says that only seven of these deaths have been confirmed as swine flu cases.

If the child in Texas is found to have been infected, the WHO is more likely to raise its pandemic alert level to phase five – the second highest and the first at which a pandemic is officially declared – as early as today.

Phase five would mean that the virus is spreading between people in at least two countries in a sustained way. A full phase six global pandemic would be declared if it was seen to be taking root in different regions of the world.

Earlier today, Germany announced its first cases of the feared new flu strain. It was the eighth country to detect it and the third in Europe. Other cases have been confirmed in Canada, New Zealand, Israel and Spain.

Results are expected today on swab samples from seven people who have displayed flu-like symptoms after coming into contact with a Scottish couple who were both infected during their honeymoon in Mexico. Sky News reported today that the seven had all tested negative, meaning that there has been no confirmed re-infection on British soil.

Mr Brown said that the Scottish couple, Iain and Dawn Askham, were responding well to treatment at the Monklands Hospital in Airdrie, Lanarkshire.

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