BEIJING: Chinese schools opened nationwide for a new term Wednesday with thousands of police and safety officers deployed to ensure security following a string of deadly attacks on young students.

The central government has instructed kindergartens and schools to beef up security and put in place video surveillance and alarm systems to guard against any further attacks.

At least six attacks on schoolchildren have taken place this year in various parts of the country, most of them between March and May.

Twenty people were killed -- including 18 children -- and more than 80 injured, according to state media reports.

Two attackers have already been executed and two others committed suicide. Another suspect was sentenced to death in June. The man who allegedly carried out the last assault in August has been detained.

State media reports have described the attackers variously as psychologically disturbed individuals or people lashing out over personal grudges, and speculated that some of the attacks may have been copycat acts.

Authorities in Chongqing have deployed 45,000 police and security guards at schools across the huge southwestern municipality, Xinhua news agency said, while the southeastern province of Fujian has deployed more than 22,000.

Beijing has sent about 2,000 specially trained safety personnel, uniformed and wearing helmets and knife-proof vests, to schools in the capital, it said.

About 220 million primary and middle school students will resume classes Wednesday.

BDST: 0910 HRS, September 1, 2010