Thailand on Wednesday defended its efforts to stop human trafficking after the United States kept it on a trafficking watch list and urged U.S. officials to visit the country and see first hand its efforts.

Thailand is a regional center for migrant workers who come from poorer, neighboring countries including Myanmar, Laos and Cambodia in search of jobs.

Rights groups say millions are vulnerable to abuse, including forced labor, in various Thai sectors including the country’s multi billion dollar seafood industry.

The 2017 Trafficking in Persons (TIP) report said Thailand reported more investigations, prosecutions and convictions of trafficking cases but it did not demonstrate “increasing efforts compared to the previous reporting period”.

It added that Thailand did not “convict officials complicit in trafficking crimes, and official complicity continued to impede anti-trafficking efforts”.

“What I want to see is perhaps more cooperation from the U.S. and for them to come to study what we have done so far,” government spokesman Weerachon Sukondhapatipak told Reuters on Wednesday.

“Maybe they will see our progress differently,” he said.

Earlier in the year, Thailand said it hoped to be upgraded from the Tier 2 watch list of nations not meeting minimum standards to end human trafficking.

In 2016 the United States removed Thailand from its list of worst human trafficking offenders, known as Tier 3, following efforts by the military government to fight trafficking in response to international criticism, including through reforms of its anti-trafficking laws.

In 2015 Southeast Asia saw more than 4,000 migrants land on the shores of Indonesia, Malaysia, Thailand and Bangladesh following a Thai crackdown on people-smuggling gangs.

Some of those arrested in the crackdown are on trial in Bangkok in what has been called the largest human trafficking trial in Thai history. A verdict is expected next month but rights groups say the arrests were just the tip of an extensive smuggling and trafficking network.

Thailand is Washington’s oldest ally in the region, but ties were strained by a 2014 military coup that ousted an elected civilian government.

Since the election of U.S. President Donald Trump, however, relations between the two nations appear to have improved, with Trump inviting Prime Minister Prayuth Chan-ocha to visit the White House.

In the 2017 TIP report the State Department placed China on its global list of the worst offenders in human trafficking and forced labor. It upgraded Myanmar to the Tier 2 Watch List.

(Reporting by Amy Sawitta Lefevre, Panarat Thepgumpanat and Panu Wongcha-um; Writing by Amy Sawitta Lefevre; Editing by Michael Perry)