Pro-democracy representatives from the Vietnamese community have met White House officials in Washington in advance of the upcoming visit by the Communist party chief, Nguyen Phu Trong.
Reports from Washington said the activists called on the National Security Council to increase pressure on Vietnam over its violations of human rights.
Mr Trong is expected to meet President Obama next week during the first ever visit to Washington by a General-Secretary of the Vietnamese Communist party.
The activists, including members of the outlawed Vietnamese democracy party, Viet Tan, want the US to call for an end to the persecution of civil society groups.
They’re reported to have warned that Vietnam has a record of reneging on promises to improve human rights.
One of the representatives, the Vietnamese-American community activist, Nguyen Quoc Quan, said the US would only find a true ally in Vietnam after the country became democratic, according to US media reports.
The visit to Washington by Mr Trong is seen as highly symbolic at a time when Vietnam is looking for friends to counter-balance the growing threat from China.
Analysts have cautioned against expectations of major agreements.
The communist leadership remains extremely wary of US intentions and suspects it of attempting to encourage domestic dissent to weaken the party’s grip on power.
Vietnam appears eager to send a message to Beijing over rising tension in the South China Sea, but remains anxious to avoid too tight an embrace from the United States.