(CNN) -- A gay couple in Malawi, found guilty of gross indecency and unnatural acts after they took part in an "engagement ceremony," was sentenced to 14 years in prison Thursday.

Steven Mojenza, 26, and Tiwonge Chimbalanga, 20, were convicted in a court Tuesday.

The pair was arrested in December at their home in Blantyre, Malawi, for professing their love in a traditional engagement ceremony. They were rounded up after news reports surfaced, charged under colonial-era sodomy laws and detained at Chichiru Prison without bail.

The arrests received some popular support in the conservative southern African nation, but sparked condemnation by gay rights activists. Human rights groups including Amnesty International and Human Rights Watch have called for the release of the couple.

Critics on the scene and condemned the sentence.

"There was no victim in this case, yet they were given a very harsh sentence by the judge," said Gift Trapence, executive director of a Malawi human rights group.

Trapence said the majority of Malawians supported the verdict, but feared the harsh sentence would push much of the country's gay community further underground.

"This sentence sends a strong and unacceptable message that discrimination is legally justified in the Malawi justice system," said Michelle Kagari, deputy Africa program director at Amnesty International, in a written statement.

Amnesty International said the couple told their attorneys they were beaten by police while in custody.

British officials said in a joint statement they were "deeply dismayed" at the couple's conviction, as well as allegations they were mistreated in police custody.

"Malawi has made significant progress on human rights in recent years," said Henry Bellingham, Foreign Office under-secretary, along with Stephen O' Brien, parliamentary under-secretary of state at the Department for International Development, and Lynne Featherstone, minister for equality at the Home Office. "The government has signed up to international human rights treaties and Malawi's constitution protects the rights of all its citizens. Infringement of these rights is intolerable. The conviction and sentencing ... runs counter to a positive trend."

In Washington, White House Press Secretary Robert Gibbs said the United States condemned the conviction and sentencing.

"The criminalization of sexual orientation and gender identity is unconscionable, and this case mars the human rights record of Malawi," he said. "We urge Malawi and all countries to stop using sexual orientation or gender identity as the basis for arrest, detention, or execution."

Philip J. Crowley, assistant secretary of state for public affairs, said "the United States is appalled" by the conviction and sentence, which he called "a significant step backward for the government of Malawi's human-rights record. Malawi must abide by its human-rights obligations."

Decriminalization of homosexuality is key not only to the protection of universal human rights, but is also "crucial to the urgent need to fight the spread of HIV/AIDS," he said.

Homosexuality is illegal in Malawi -- as it is in most African nations -- and government officials have said they are simply upholding the law.

But activists in Malawi say Article 20 of the country's constitution -- which outlaws discrimination -- is being violated. The Malawi Law Society said the prosecution of the two men has been driven by prejudice -- not jurisprudence.

Anthony Kamanga, Malawi's solicitor general and secretary for justice and constitutional affairs, said the law does not conflict with the constitution, and denied the charge of prejudice.

"I do not think that in this particular case that these two people were prejudiced against," he said. "We have no law that criminalizes sexual orientation, just certain sexual acts."

Kamanga said the criticism is unfair.

"For some reason, this case has been blown out of proportion," he charged. "The courts have been fair to these two men."

"Most people are repugnant towards homosexuality," said Canaan Phiri, secretary general of the Malawi Council of Churches. "People do not declare their homosexuality because people are against this."

Ahead of the verdict, the two men thanked their supporters, remaining defiant in a statement released through Tatchell.

In it, Chimbalanga said: "I love Steven so much. If people or the world cannot give me the chance and freedom to continue living with him as my lover, then I am better off to die here in prison. Freedom without him is useless and meaningless."

CNN's David McKenzie contributed to this report.