China's judicial authorities said Sunday the country had maintained "high pressure" on corruption to press on with an anti-graft drive lasting more than three years.

A total of 22 Chinese former officials at ministerial level or above, including former Chinese leader Zhou Yongkang, were prosecuted in 2015, while 41 were subject to investigation, a report on the work of the Supreme People's Procuratorate (SPP) read.

Another report on the Supreme People's Court, meanwhile, said courts had concluded trials for Zhou and 15 other senior officials, showcasing "the Party and the country's resolute determination in cracking down on corruption," it said.

Both reports were made public on Sunday morning, shortly before a plenary meeting of the annual session of China's top legislature.

1,419 criminals convicted of harming state security

Chinese courts convicted 1,419 criminals of harming state security, including taking part in terrorist attacks and secessionist activities, in 2015, Chief Justice Zhou Qiang said on Sunday.

Chinese courts concluded the trial of 1,084 cases involving crimes that threatened state security, Zhou told a plenary meeting of the ongoing session of the National People's Congress (NPC).

Last year, courts stepped up efforts against criminals who instigated secessionist activities; who led, organized and took part in terrorist groups; and who spread video and audio products about terrorism, he said.

Zhou pledged in the report that courts will well implement the laws on state security and counter-terrorism and severely punish terrorists and secessionists.

About 31,000 prisoners released in 2015

A total of 31,527 prisoners in China were released early last year thanks to an amnesty deal.

The report was delivered by Chief Justice Zhou Qiang at a plenary meeting of the ongoing session of the National People's Congress.

The amnesty was adopted by China's top legislature and signed by President Xi Jinping on Aug. 29, 2015, before a national commemoration of the 70th anniversary of the end of World War II.

The pardoned prisoners, including war veterans, and the very old, young or infirm prisoners, had been released by the end of 2015 as scheduled.

According to the deal, four categories of prisoners were eligible for consideration:

-- Criminals who fought against Japanese invasion in the WWII and the civil war against the Kuomintang (KMT).

-- Criminals who participated in wars to safeguard national sovereignty, security and territorial integrity after 1949, with the exception of those found guilty of serious crimes including graft, terrorism and organized crime, as well as repeat offenders.

-- Criminals who are 75 or above, and those with physical disabilities who are unable to care for themselves.

-- Those who committed crimes while under the age of 18 and received a maximum sentence of three years in prison, or have less than a year left to serve, with the exception of those convicted of homicide, rape, terrorism or narcotics offences.

Of the pardoned prisoners, 50 belong to the first category, 1,428 belong to the second, 122 to the third and 29,927 to the fourth.

"We managed to release everyone that is eligible and not to let go of anyone that should not be," Zhou said.

The amnesty was the eighth since the founding of the People's Republic of China in 1949, 40 years after the last one in 1975.

It indicated China's commitment to the rule of law and humanitarianism, Zhou said.