By Jessie Pang

HONG KONG (Reuters) -A Hong Kong appeal court on Monday blocked jailed media tycoon Jimmy Lai's bid to challenge in the city's highest court a warrant obtained by national security police to scrutinise the contents of his mobile phones.

Lai, 75, is the founder of the now shut pro-democracy newspaper Apple Daily and is due to face trial in September on three charges under the city's sweeping national security law, including collusion with foreign forces. He also faces a charge under the British colonial-era sedition law.

Lai is one of the most prominent Hong Kong critics of China's Communist Party leadership, including President Xi Jinping.

The tycoon has been challenging police scrutiny of two of his mobile phones seized during his arrest at his home in August 2020, partly on the basis that they contained journalistic material.

The High Court rejected challenges in August and October last year, when Lai's lawyers argued that such searches could have a "chilling effect" on Hong Kong's press freedom.

Three Court of Appeal judges on Monday ruled that they could not allow Lai's lawyers to appeal to Hong Kong's highest court as they had raised points not covered earlier and had "failed to make a proper case".

Even though police had already searched the phones, the issues involved "great public interest", his lawyers had argued.

It is not clear if Lai's legal team would attempt any further steps.

Lai lost a bid to end his national security trial in May. He could spend the rest of his life in prison if convicted.

Beijing imposed the national security law on Hong Kong in 2020 after months of anti-government protests. The law punishes acts including subversion, collusion with foreign forces and terrorism with up to life in prison.

Critics say the law is part of an effort by Beijing to end dissent and freedoms guaranteed to the city for 50 years when it was handed over to China from British rule in 1997.

Beijing and the city's government say the law is needed to preserve the stability that underpins the financial hub's economic success.

Lai is already serving a five year, nine month sentence for fraud after his conviction for violating a lease contract for the Apple Daily's headquarters. He denied the charge.

(Reporting By Jessie Pang; editing by Greg Torode, Robert Birsel)