HONG KONG — Hong Kong’s leader denied on Monday that there was any political interference in a court’s decision last week to send three young pro-democracy protest leaders to jail in the Chinese-controlled city.

“Our courts are exercising judicial powers independently, free from any interference,” Hong Kong Chief Executive Carrie Lam said at a news conference called a day after tens of thousands of people rallied to protest the sentences given the three leaders.

“There’s absolutely no political interference both in the prosecution, in the review of sentence and in the judgments and rulings handed down by the Court of Appeal,” she said.

The court overturned an earlier verdict that had allowed the three activists to avoid prison.

The activists — Joshua Wong, Nathan Law and Alex Chow — were accused of joining or leading an unlawful assembly that sparked huge pro-democracy protests in 2014. Youthful activists brought major thoroughfares to a standstill for 79 days in the non-violent “Umbrella Movement” movement protesting Beijing’s plan to restrict elections in the semi-autonomous region.

Wong, Chow and Law were sentenced to six, seven and eight months in jail respectively after the justice secretary requested a review of the lower court’s verdict last year, which let them off with community service or a suspended sentence. They will also be blocked from seeking public office for five years.

The case raises fears that Hong Kong’s independent judiciary is under threat as the city’s Beijing-backed government uses the courts to clamp down on the opposition and constrain its ability to protest.

Lam rejected accusations by rights groups and pro-democracy supporters that the imprisonment of the three, aged 20 to 27, amounted to political persecution, saying that the case involved “unlawful acts or even acts involving violence.”

Under the “one country, two systems” format that took effect after the 1997 handover of Hong Kong from Britain, Beijing promised to let the city keep its wide autonomy and civil rights such as freedom of speech and protest unknown on mainland China. But many residents and analysts fear China’s Communist leaders are backtracking on their promises.