HANOI—U.S. Secretary of State Hillary Clinton publicly pressed Vietnam to further open its political system amid concerns about the Communist government's crackdown on democracy activists and the Internet.

U.S. Secretary of State Hillary Clinton met with Asean ministers in Vietnam, seeking support for South Korea in response to deadly torpedo attack.

Mrs. Clinton made her comments Thursday during a two-day visit to Hanoi aimed, in part, to herald the strengthening U.S.-Vietnam relationship 15 years after the two nations normalized ties. The American envoy said growing ties between Washington and Hanoi could serve as a model for reconciliation among former wartime foes.

Still, Mrs. Clinton emphasized that Vietnam's emergence as an Asian economic power depends on its willingness to open its political system. The American envoy said that Hanoi, even as Washington's friend, should expect to face pressure from the West on human rights.

"It is true that profound differences exist, particularly over the question of political freedoms," Mrs. Clinton told a lunch on Thursday honoring the restoration of U.S.-Vietnam relations. "The United States will continue to urge Vietnam to strengthen its commitment to human rights and give its people an even greater say over the direction of their own lives."

Vietnamese Foreign Minister Pham Gia Khiem, appearing with Mrs. Clinton at a press event earlier Thursday, praised Vietnam's shared interests with the U.S. but also pushed back on Washington's criticism of Hanoi's respect for civil liberties.

"Human rights have common values but ... it depends a lot on the cultural and historical background," Mr. Khiem told reporters at Hanoi's Foreign Ministry. "Human rights cannot be imposed from the outside."

Secretary of State Hillary Clinton, speaking in Hanoi on Thursday, urged Vietnam to strengthen its commitment to human rights. Agence France-Presse/Getty Images

Criticism of Vietnam's human-rights record has intensified recently as Vietnamese authorities have arrested several dissidents. Authorities have detained roughly a dozen human-rights activists and critics over the past year, including four prominent campaigners who were sentenced to lengthy prison terms in January after being convicted of attempting to overthrow the government.

One of those dissidents, a U.S.-trained human-rights lawyer named Le Cong Dinh, was given a five-year sentence after admitting in court that he had broken the law by joining a banned political party.

The government also has instructed Internet-service providers to block access to social-networking web sites such as Facebook over the past year, prompting concerns that some international companies might be scared off by the tightening controls.

In December, U.S. Ambassador Michael Michalak told a donor conference that the Internet curbs were hindering the expansion of commerce in Vietnam. A bipartisan group of U.S. lawmakers this month pressed Mrs. Clinton in a letter to publicly raise Hanoi's human-rights record during meetings with Vietnamese officials.

Clinton Tours Asia

Mrs. Clinton is visiting Hanoi both to commemorate normalized relations and to take part in a regional security conference involving Southeast Asian counties, China and Japan. It is her first visit to Hanoi since she accompanied her husband, former U.S. President Bill Clinton, on a tour of Vietnam in 2000.

The U.S. restored diplomatic ties with Vietnam in 1995, one of the Clinton administration's signature foreign-policy achievements. More than 50,000 Americans and an estimated one million Vietnamese died during the decade-long Vietnam war that ended in 1975.

Mrs. Clinton lauded Vietnam's economic growth and its commitment to cooperating with Washington on financial, strategic and environmental issues. She visited an AIDS clinic funded by the U.S. government in Hanoi Thursday and took part in a development forum aimed at bolstering the economies of Vietnam, Cambodia and Laos.

"We have learned to see each other not as former enemies but as actual and potential partners, colleagues and friends," Mrs. Clinton said, referring to improving U.S.-Vietnam relations. "We will continue to choose engagement and cooperation over escalation and division."

Bilateral trade between the U.S. and Vietnam has blossomed in recent years and surpassed $15 billion in 2009. The Southeast Asian country is the U.S.'s second-largest supplier of clothing.

Issues related to the Vietnam War, however, continue to affect the relationship. A Vietnamese journalist pushed Mrs. Clinton Thursday to do more to address the continuing health consequences for the Vietnamese people of the 11 million gallons of Agent Orange and other toxins dropped on south Vietnam by American warplanes between 1962 and 1971.

"We have been working with Vietnam for about nine years to try to remedy the effects of Agent Orange," Mrs. Clinton said. "[We plan to] increase our cooperation and make even greater progress together."

Secretary of State Clinton, speaking in Hanoi on Thursday, urged Vietnam to strengthen its commitment to human rights. Associated Press

Vietnam's hard line on political freedoms has disappointed investors and diplomats who expected the country to open up further as it integrated more with the global economy. The government gradually increased space for public debate and religious worship over the past decade, partly to smooth Vietnam's entry into the World Trade Organization in 2007, analysts say.

Since then, Vietnam has had to grapple with economic challenges including a destabilizing spike in inflation in 2008 and several currency devaluations. Although growth has remained strong compared with most Western economies, some analysts say the hiccups have emboldened conservative elements within Vietnam's ruling Communist Party as it prepares for a crucial party congress early next year to chart policy for the following five years. Many analysts say jockeying between conservative and reformist factions before the congress has contributed to the more hostile environment in the country.

—Patrick Barta in Bangkok contributed to this article.

Write to Jay Solomon at jay.solomon@wsj.com