Singapore has taken issue with an annual report by the US State Department for depicting an inaccurate and less positive picture of the human trafficking situation here.

An inter-agency task force co-chaired by the Home Affairs and Manpower ministries said there were 17 sex and labour trafficking victims identified last year, lower than the 33 cited in the Trafficking in Persons (TIP) report.

The task force also disputed the number of trafficking suspects prosecuted and convicted.

Released last month, the US report said Singapore prosecuted eight suspects for sex and labour trafficking and convicted two trafficking offenders last year. However, Singapore said there were five prosecuted and three convicted.

"This information (from the task force) had been made available to the US State Department prior to the publication of the US TIP Report 2017," said the task force spokesman.

In response to Singapore's remarks, the US State Department's Office to Monitor and Combat TIP said its assessment was in line with information from the authorities and civil society entities here.

The US spokesman said low-wage migrant workers worldwide have been identified as a demographic group at particularly high risk of being trafficked. It added that it was concerned that workers here were hesitant to report issues such as unpaid wages and high debt bondages, which it said were indicators of trafficking.

"Each year we strive to publish a product that most accurately captures the anti-trafficking efforts of any given country," said a spokesman, adding it was open to discussing amendments or clarifications to ensure the "most accurate assessment of Singapore's efforts".

According to the report, Singapore continues to remain on the Tier 2 list, with countries like Indonesia and Vietnam. A Tier 2 listing means the country does not meet US norms in combating trafficking but is making effort. Tier 1 is designated to nations that meet minimum US standards.

Singapore also took issue with "misrepresentations" in the report stating there were "large numbers of migrant workers (who) experience conditions indicative of labour trafficking" here.

The task force spokesman said: "It is not clear what the US' basis is for making such an assertion."

In response, the US spokesman said low-wage migrant workers worldwide have been identified as a demographic group at particularly high risk of being trafficked.

It added that it was concerned that workers here were hesitant to report issues such as unpaid wages and high debt bondages, which it said were indicators of trafficking.

The discrepancies highlighted could be a result of different methodology or the wide definition given to trafficking, said law professor Kumaralingam Amirthalingam, noting that the data sources for the US and Singapore were different.

According to the United Nations TIP Protocol, which Singapore has adopted in the Prevention of Human Trafficking Act enacted in 2015, human trafficking is defined by three factors: There has to be an act - such as recruiting or harbouring; a means - usually via force or deception; and it has to be for the purpose of exploitation.

"You need the broad definition to drive international treaties and policy, but when it comes to enacting criminal law, broad laws can be dangerous because it might lead to over-criminalisation," said Prof Kumaralingam.

He added that in other nations, there have been cases that would ordinarily come under pimping or prostitution, but have been tried under trafficking of persons.

"The value in human trafficking laws is that it sends a strong signal that the offence is serious... If any domestic crime that technically satisfies the human trafficking definition is treated as trafficking, the law might lose its significance."

Correction note: This story has been edited for clarity.