The US is putting pressure on Gambia over two missing US citizens and new legislation criminalising homosexuality, as well as possible human rights abuses against opponents of the government.

Concerns were raised by Barack Obama's National Security Council over moves to stop United Nations human rights investigators accessing the country.

It also challenged support for the persecution of members of the lesbian, gay, bisexual and transgender community.

Gambia's foreign minister last week vowed to sever dialogue with the European Union after the bloc, an important donor to the West African nation, raised similar criticisms.

"We remain concerned about ongoing reports of forced disappearances and arbitrary arrests, including of journalists, human rights advocates, and civil servants," NSC Spokesperson Bernadette Meehan said.

In the statement, released on Thursday and read on Gambian state-owned radio and television, the NSC said it was disappointed in the Gambian government's failure to investigate the disappearance of two US citizens missing since June 2013.

Though the statement did not name the missing Americans, it was apparently referring to Alhaji Ceesay and Ebrima Jobe, two Gambian-born US citizens, who had travelled to the capital Banjul to look into opening a computer business.

During a visit to Gambia last month, the UN's investigators for illegal killings and for torture heard allegations of extrajudicial executions of government opponents, journalists and activists and the widespread use of torture.

However, they said they were prevented from visiting parts of the main prison in Banjul despite earlier receiving approval.

President Yahya Jammeh - a former military officer who seized power in a 1994 coup - signed into law legislation in October that introduced the crime of 'aggravated homosexuality', making it punishable in some cases with life in prison.

The definition covers cases such as homosexual relations with someone under the age of 18, or a person with HIV having homosexual sex.

The UN High Commissioner for Human Rights, has said Gambia's new law violates fundamental human rights and has called for its repeal. Rights watchdog Amnesty International says more than a dozen people have already been arrested under the legislation.

The NSC criticised the law and said it was concerned by calls by senior officials for the persecution of members of the lesbian, gay, bisexual, and transgender community.

"Protecting human rights and fundamental freedoms is a cornerstone of US foreign policy, and we will be guided by these values as we respond to these negative developments in The Gambia," it said.

Gambia's government did not immediately respond to the NSC statement.