HANOI — A Vietnamese court on Tuesday sentenced an activist to nine years in prison on charges of producing videos that defamed the country’s leadership, in the latest crackdown on dissent.

Tran Thi Nga was convicted of spreading propaganda against the state in the one-day trial at the People’s Court in Ha Nam province in northern Vietnam, her lawyer said.

Nga, 40, campaigned against environmental pollution, police brutality, and illegal land confiscation, and called for a tougher stance toward China’s assertive territorial claims in the South China Sea.

Nga maintained her innocence during the trial, saying she did not oppose anyone, but was only against corruption and injustice, her lawyer said.

The lawyer said there was no proof that 13 videos used against Nga in the trial — 11 taken from the Internet and two allegedly found on her computer — were hers.

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