She is released after serving four years of a seven-year sentence for leafleting in support of workers.
He had called online for the country's national leaders to resign.
Leaders of the two countries stick to their positions during high-level discussions in Hanoi.
Experts say the two sides will look to calm tensions in the South China Sea.
A Chinese envoy asks Ban Ki-moon to circulate documents outlining Beijing's position.
Officials accuse China of lying about the incident.