Figures for 2012 show 154 reported cases of racist violence, including 25 in which victims said perpetrators were police

The number of racially motivated attacks increased in Greece last year, as did the severity of the violence involved, human rights groups have said.

The Racist Violence Recording Network reported 154 cases of racist violence in 2012, including 25 in which the victims said the perpetrators were police. The figures were released a week after more than 30 Bangladeshi workers suffered shotgun wounds on a strawberry farm in southern Greece during a dispute with foremen over back pay.

Kostis Papaioannou, the head of the National Commission for Human Rights, said the number of attacks recorded had increased 20% from the previous year. But, he noted, the true number could be much higher because many victims are afraid to come forward, fearing further mistreatment by authorities or deportation for entering the country illegally.

There have been numerous reports of police, who are at the forefront of a government crackdown on foreigners in the country illegally, mistreating immigrants during routine document checks on the street or during detentions. The police have repeatedly said they investigate all reported cases of mistreatment.

The network, composed of 30 aid and human rights groups, records cases only when it has spoken to the victim themselves.

The 2012 figures show "some very interesting and very worrying tendencies regarding racist violence in Greece", Papaioannou said. "We have both an increase in the numbers of attacks but also – which is really worrying too – we have an escalation in the intensity of this violence."

The incidents have spiralled as Greece's economy has worsened over the past few years. Relying on international rescue loans to remain solvent, the country has imposed deep spending cuts that have sent unemployment soaring to around 27%.

The vast majority of attacks occurred in Athens, mainly in inner city neighbourhoods. Immigrants are often set upon by groups of men wielding metal bars, chains, brass knuckles, broken bottles, knives and wooden clubs. The victims suffer from broken bones, damage to sight and hearing and extensive bruising, the network said.

One fatality was recorded last year – a 31-year-old Egyptian man who died of head injuries 17 days after falling into a coma following a severe beating, the network said.

Reza Golami, the head of an association of Afghans living in Greece, said many migrants have become too afraid to leave their homes.

"There live with fear inside them, whether it's the fear of the police or the fear of racists," he said. "They don't dare leave their homes to buy a loaf of bread. This is not something that affects men alone, but even women and small children. We have witnessed hundreds of such cases."

Authorities have vowed to crack down on hate crimes in the financially struggling country. Greece is main entry point for migrants entering the EU illegally, and there has been a surge in popular support for Golden Dawn, an extreme-right xenophobic party, as the financial crisis has deepened.

The government has set up a special unit within the police to deal with racist crimes – a move the rights groups welcomed but said didn't go far enough.