Parents who take their daughters abroad to undergo female circumcision will
face up to 14 years in jail under new measures that have come into force.
David Blunkett said communities must help to enforce the measures
Some ethnic minority communities have evaded the law by arranging for girls to have the operation abroad.
But the Female Genital Mutilation Act makes this illegal.
"No cultural, medical or other reason can ever justify a practice that causes
so much pain and suffering," Home Secretary David Blunkett said.
'Very harmful practice'
He was speaking at a support centre in north-west London, after he and Home Office minister Baroness Scotland met some women who have undergone circumcision.
"Female genital mutilation is a very harmful practice that is already rightly illegal in this country," he said.
"Regardless of cultural background, it is completely unacceptable and should be illegal wherever it takes place.
"The legislation which comes into force today will close a loophole in the previous law by preventing people taking young girls abroad to carry out female genital mutilation and bring us closer to eradicating this practice entirely."
Mr Blunkett said he expected to see prosecutions as a result of the new law.
Protecting women from genital mutilation could also be taken into account in asylum claims by women, he said, providing they followed official routes to enter the country.
He stressed that enforcing the law would rely on the vigilance of teachers, health and social workers, in partnership with voluntary organisations and the communities involved.
"They must be brave enough to take it head-on," he said.
Campaigners say the number of cases they see in the UK is rising
"Where doctors come across this kind of mutilation, they have a duty to take actions in reporting it but also to help the young people themselves."
Female genital mutilation involves surgically removing the clitoris and sometimes parts of the labia.
Experts believe 74,000 first-generation African immigrant women in the UK have undergone female circumcision.
Rahmat Mohammad, of the women's rights group Forward, said an estimated 7,000 girls in the UK were currently at risk of being forced into the procedure.
'Support the parents'
She believes the number of cases Forward sees is rising despite a long-running campaign in UK communities.
She said: "We don't want a law where it is used to remove the child from the parents; we want to be able to support the parents so they will protect their own children."
Circumcision is usually performed on girls between four and 13 years old, but can be inflicted on newborn babies or young women before marriage or pregnancy.
Reasons given include custom and tradition, religious demand, hygiene and prevention of promiscuity.
Mr Blunkett gave government backing to a private member's bill, introduced by Ann Clwyd MP, amending the law to make it unlawful to take girls abroad for "female genital mutilation".
It increased penalties from five to 14 years' imprisonment.
Female genital mutilation is common among Somali, Ethiopian, Eritrean, Yemeni, Malaysian and Indonesian communities.