Almost a year after a deadly earthquake devastated part of China's Sichuan province, the Chinese authorities have released official figures on the number of students killed in the disaster.

It says of the estimated 68,000 who died and 18,000 listed as missing as a result of the disaster, 5,335 were students.

Many of the children were killed in their classrooms, when their schools collapsed during the quake which struck in the middle of the day on May 12, 2008.

Across the disaster zone, hundreds of schools were flattened by the quake, while other buildings nearby remained standing and their occupants survived.

That has led to allegations from bereaved parents that corruption and shoddy building work meant the schools were unsafe.

Some have said materials meant for school construction projects were sold on the side by contractors for personal gain, meaning the buildings were weak and did not meet safety codes.

'Politically-charged issue'

Al Jazeera's Beijing correspondent, Tony Cheng, says the number of children killed in collapsed schools has become a politically charged issue and, despite considerable public anger, there has been very little government investigation.

Officials have blamed the sheer power of the quake as the main cause of the number of flattened schools.

In a transcript of Thursday's news conference at which the Sichuan government announced the death toll, officials said that an inquiry would be ordered if there was solid proof of flaws in construction work.

"Once there is concrete evidence to prove that problems exist in building designs and construction, relevant departments will investigate according to law," it said.

The announcement came as a report in the official China Daily newspaper said that a government circular had ordered that safety controls over the construction and rebuilding of schools be strengthened.

The circular said there would be severe punishment for those who engage in illegal practices, the report said.

With the one year anniversary of the quake approaching next week, our correspondent says there have been reports that some parents have been prevented from returning to the scene of their children's deaths.

Many parents who lost children in the disaster have petitioned and protested calling for a proper investigation into school building standards, only to be detained or warned against speaking out.

Activists sympathetic to their cause have also been harassed or taken away by police.