The four police officials were arrested for corruption in connection with drug trafficking.
Hun Sen was responding to concerns raised by the US lawmakers as the refugee center nears its closing date, Feb. 15.
The decision overruled a ruling by the Phnom Penh Municipal Court last week to hold five of seven Thais arrested in December.
The four men were charged under Article 38 of the 1992 penal code and face up to seven years in prison if convicted.
Protesters had prepared a letter for the embassy, but embassy officials would not accept it.
The recent midterm elections in US Congress should serve as a good model for Cambodians on how power can be shifted smoothly.
Government ministry officials have until March to add up their worth and send it to anti-corruption authorities.
Some NGOs say they fear the law will be used as a tool of repression against anti-government groups.
Thai lawmaker Panich Vikitsreth and Narumol Jitrawarattana, were released after they paid their bail, approximately at $250 each.
The seven Thais, including a member of parliament, are facing a potential prison sentence of 18 months, for illegal entry into Cambodia.
Hun Hean was removed from his post following the January 7 holiday celebrations.
Jan. 7 remains a contentious day for Cambodians, marking both the ouster of the Khmer Rouge and the beginning of Vietnamese occupation.