Ahead of President Obama's visit to Vietnam later in the month, Tom Malinowski, US assistant secretary for democracy, human rights and labor, will visit the country next week. He will meet Vietnamese officials on 9 and 10 May and urge them to make progress on human rights issues.

The meeting is expected to prepare the ground for President Barack Obama's visit to Vietnam later in the month.

Malinowski will take up the issue of political prisoners during his talks with Vietnamese officials. "Among other things, he will urge Vietnam to release political prisoners without condition and encourage further reforms that will help to make Vietnam's laws consistent with its international human rights obligations," the State Department said.

Earlier, in April, Malinowski had said the US was monitoring Vietnam's legal reforms, especially laws that had a close bearing on human rights, such as those on demonstrations, non-government groups and religion that Vietnam's National Assembly is due to take up this year.

The frosty relations between the two countries have thawed only in recent years. In October 2014, the US partially lifted the prohibition on lethal arms sales to Vietnam, despite severe criticism by several rights groups. However, the communist government's treatment of political opponents and workers still remains a bone of contention between the two countries.

Vietnam has always denied the allegations made by human rights organisations about unfair laws, media restrictions and mistreatment and torture of prisoners. Hanoi has maintained it has not jailed any religious, political or media persons and has only put criminals behind bars.

Vietnamese officials had earlier expressed the hope that Obama's visit would pave the way for the complete lifting of the lethal weapons ban.