A dissident Vietnamese blogger known by her pen name, Mother Mushroom, has arrived in the US after her surprise release from prison, telling a large crowd of supporters she will “never keep silent” in her fight for democracy in the one-party state.

Nguyen Ngoc Nhu Quynh, 39, was quietly freed from a Vietnamese jail on Wednesday and put on a plane with her elderly mother and two young children who were seen smiling and hugging her.

Her unexpected release after two years behind bars came as the US defence secretary, General James Mattis, visited Vietnam as part of an effort to warm ties between the former foes, both eager to counter China’s rising influence in Asia.

Neither the Pentagon nor the Vietnamese government commented on the timing of Quynh’s release, though the US embassy in Hanoi said it welcomed the move.

The outspoken blogger, whose name comes from her daughter’s nickname “mushroom”, smiled and spoke to a large crowd of friends and supporters, many livestreaming on Facebook the chaotic scene when she arrived at Houston’s George Bush airport just before midnight on Wednesday.

Quynh said leaving her country was not an easy move but vowed to “never keep silent” in her fight for human rights back home.

Nguyen Ngoc Nhu Quynh during her trial in Vietnam’s Khanh Hoa province. Photograph: Tien Minh/AP

“I will continue to raise my voice until there is human rights in Vietnam, real human rights,” she said.

Quynh has been behind bars since being arrested in 2016 while visiting a fellow activist in prison.

She was later convicted for “anti-state propaganda” for publishing damning Facebook posts about deaths in police custody, a toxic spill in central Vietnam and criticisms of the ruling Communist party.

The blogger was sentenced to 10 years in jail last year, a heavy ruling that drew swift rebuke from the US, the EU and the UN.

Earlier this year, her move to a prison hundreds of kilometres from her home town Nha Trang in central Vietnam took a toll on her family who were exhausted by the travel.

“It was time for me to think of my family, I made this final decision (to leave) for the future of my two kids,” she said.

The US embassy in Hanoi said Quynh had requested to go to the US if released and urged Vietnam to free other activists.

“We will continue to call on the government of Vietnam to immediately and unconditionally release all prisoners of conscience,” the embassy spokeswoman Karen Tang said.

Quynh’s arrest grabbed headlines globally after receiving the International Women of Courage award in 2017, presented to her in absentia by the US first lady, Melania Trump.

But Donald Trump’s administration has come under fire for not doing enough to protect human rights, especially in Vietnam.

Though Vietnam has long jailed its critics, a hardline leadership in charge since 2016 has been accused of redoubling its efforts to silence activists.

More than 55 bloggers, protesters and Facebookers have been jailed this year alone, with the length and frequency of sentences steadily rising.

Soon after Quynh was released Wednesday, a fellow dissident Nguyen Dinh Thanh, 27, was jailed for seven years for “spreading anti-state materials” in the southern Binh Duong province.

According to state media the former medical student was accused of printing 3,000 leaflets, apparently to be distributed at nationwide protests in June.

In another indication that Vietnam is not likely to let up its punishment of critics, the activist Le Dinh Luong had his 20-year sentence upheld in an appeal trial on Thursday in Nghe An province.