SINGAPORE - The family of the American student detained in Vietnam over his alleged involvement in a June 10 protest are requesting "a clear and insightful explanation" on his confession video.

On Monday (June 18), William Nguyen, 32, had appeared on Vietnamese state television expressing regret for breaking the law, and promising to stay away from future rallies.

Speaking to The Straits Times on Wednesday, Nguyen's sister Victoria expressed concern about what she described as a "lack of urgency" from the US State Department in handling his case.

She noted that it remains unclear if her brother will be released, and said she has not heard from the State Department since Monday afternoon (US time) after informing them of the confession video.

"We specifically request a clear and insightful explanation of the significance of the confession video," she said, adding that the family will continue to call for Nguyen's release.

Nguyen, a graduate student of the Lee Kuan Yew School of Public Policy (LKYSPP), has been held for around 10 days.

He was detained in Ho Chi Minh City after attending mass demonstrations against draft laws to develop special economic zones which would grant investors 99-year leases. Protesters feared the land would end up in the hands of China, with which Vietnam has a fraught relationship.

In response to queries, a State Department official said: "Our consular officers engaged with the Vietnamese government as soon as they learnt of Mr Nguyen's arrest. The Ambassador and Consul General have raised his case on numerous occasions with their counterparts and will continue to do so."

He added that consular officers visited Nguyen "at the first possible opportunity", and the Vietnamese government allowed them access on June 15.

" In addition, our Ambassador and other Department personnel are engaged with congressional representatives (on Nguyen's case)," he said, expressing concern over the initial treatment of Nguyen when he was taken into custody.

Video footage of the protest circulating online showed Nguyen with blood on his head, being dragged by men in plainclothes through the streets, before he was arrested.

"We have made those concerns known to Vietnamese authorities," he said.

The State Department official added that during officers' visit on June 15, Nguyen had "appeared in good health and stated he did not require medical treatment".

Nguyen was in Vietnam on a vacation ahead of his graduation from LKYSPP in July.