Diplomats gathered at the UN Human Rights Council widely condemned continued restrictions on freedom of expression, including preventing activists from attending the hearing in Geneva.
"Vietnam still harasses and detains those who exercise universal rights and freedoms, such as freedom of expression and association," US representative Peter Mulrean told the assembly, calling on the country to "release all political prisoners".
He was one of 106 diplomats who spoke at Vietnam's so-called Universal Periodic Review, which all 193 UN countries must undergo every four years.
Many hailed the communist country's progress in areas such as poverty reduction and boosting school enrolment, as well as its signature of the Convention against Torture, since its last review in 2009.
Vietnamese Vice Foreign Minister Ha Kim Ngoc insisted the one-party state, which recently became a member of the council itself, was going out of its way to encourage a "diverse emergence of the press and mass media, including the Internet".
But Sweden's Anna Jakenberg Brinck criticised "an increase in regulations to control the Internet and in harassments and arrests of netizens".
She said at least 58 people had been arrested or sentenced to prison under "vague provisions of 'national security offences' for exercising their right to freedom of expression on the Internet" since 2009.
Japan's representative recommended Vietnam do more to guarantee freedom of expression and the independence of the press, including online.
Others, including Switzerland and Britain, urged the country to rein in its use of the death penalty.
Murder, rape, serious financial crimes, and drug and arms trafficking are among the crimes carrying the death penalty in Vietnam.
Vietnam last month sentenced 30 drug smugglers to death, and is currently believed to have more than 700 prisoners on death row.
Although Vietnam does not release statistics, Amnesty International recorded 86 new death sentences in 2012 and said that five executions were carried out the previous year.
The Vietnamese vice foreign minister said at the end of the session it was a "pity that some comments were based on a lack of objective information".
Wednesday's session came just days after Dang Xuong Hung -- Vietnam's consul in Geneva from 2008 to 2012 -- said he had sought political asylum in Switzerland.
In an open letter, he called on the Vietnamese delegation at the rights council to admit to the country's violations.
"Once we dare speak the truth, we won't have to waste time dishonestly concealing the facts," he wrote.
Rights groups also decried this week that an independent journalist and civil society advocate scheduled to speak in Geneva had been blocked from leaving Vietnam.