Since Kenya sent forces into southern Somalia in October to fight the Al Qaeda-linked al Shabaab rebels, attacks have rocked the border towns of Garissa, Mandera and Wajir as well as the vast Dadaab refugee camp.

In response, security forces have raped, beaten and arbitrarily detained civilians as well as looting and destroying their property and extorting money, the New York-based rights group said in a report.

Nairobi blames the Shabaab for a series of cross-border attacks and abductions of foreigners. The hardline militia has vowed to avenge the Kenyan offensive.

"The attacks carried out by suspected al Shabaab supporters are abhorrent, but they can never justify this kind of indiscriminate abuse," said Leslie Lefkow, HRW deputy director for Africa.

"Kenyan police and soldiers ought to be protecting civilians, not assaulting them."

HRW said the worst abuses occurred in Dadaab, home to some 500 000 Somali refugees, where police stormed houses in the aftermath of an explosion there and raped at least one woman, tried to sexually assault others and beat children.

They also looted hundreds of thousands of dollars and property.

"Rather than conduct investigations to identify and apprehend the perpetrators, both the police and army responded with violent reprisals against Kenyan citizens and Somali refugees," the report said.

The rights group also in January said security forces were abusing civilians in the region that borders lawless Somalia.

"The reprisals against ethnic Somalis have contributed to increased mistrust of the security forces by North Eastern province residents," the watchdog said.

Predominantly Muslim, arid north-eastern Kenya is hugely underdeveloped and its residents have blamed the central government for marginalising the area.

HRW said the defence and the internal security ministries pledged to probe the abuses and hold those responsible accountable.