London – Many people are shot dead by police forces who do not follow United Nations standards on using lethal force only where necessary and in self-defence, Amnesty International says.

Among other countries, the human rights group singled out Jamaica, where it said police have shot dead 140 people a year on average over the last ten years, and Brazil where killings by police rose sharply in 2003. "International standards do exist to control the use of guns and other methods of force by police and law enforcement officials – but in too many countries around the world these standards are not being followed," Amnesty said on Monday.

"Too many police forces ... are trained in how to fire a gun, but not in how to decide whether it should be fired, or when," Amnesty said.

East Timor's new, UN-trained police were equipped with new guns but training had focused on how to shoot rather than how to assess threats or exercise restraint, Amnesty said.

In a report, the London-based rights group called on countries to train police fully and to incorporate UN standards into local law. It said countries should take account of how closely UN standards were followed before exporting firearms to foreign police forces.

Police and security officers had unlawfully killed civilians in more than 80 countries between 1997 and 2000, Amnesty said. Police shootings worsened the cycle of violence by undermining public trust in the police and making it less likely civilians would give up their own weapons.

"In Jamaica, which has the highest rate of police shootings per capita in the world, evidence repeatedly contradicts police claims that they were fired upon first and indicates instead a disturbing pattern of extrajudicial executions," Amnesty said.

And the group said repeated testimony from Rio de Janeiro showed police discrimination that often ended in civilian deaths.

On so-called "less-than-lethal" weapons, the report said a number of people had been killed in North America by tasers, dart-guns that stun targets with a 50,000 volt electric shock.

Amnesty called for an independent investigation into taser guns, which were used by police in the US and 17 other countries in 2002, to determine their "compatibility with human rights standards".

The report also highlighted examples of good practice. South Africa had recently changed an apartheid-era law permitting police to shoot at suspected thieves, drug dealers and fleeing suspects posing no direct threat to the lives of the police or public, Amnesty said.