Seven men who were part of a brutal paedophile ring that raped, tortured and abused vulnerable girls as young as 11 in Oxford have been jailed at the Old Bailey.

Five of the men were sentenced to life and will serve a minimum of between 12 and 20 years after one of the biggest child sexual exploitation trials in recent years.

The judge, police and CPS said that the severity of the jail terms, which are longer than those in other high-profile grooming cases such as Rochdale and Derby, sent out a message to abusers that they would be targeted and brought to justice.

Sentencing the men, Judge Peter Rook, who presided over the 18-week trial, said that they had committed "a series of sexual crimes of the utmost depravity" and had targeted "young girls because they were vulnerable, underage and out of control".

Brothers Akhtar Dogar, 32, and Anjum Dogar, 31, were given life sentences and were told by the judge that they had been found guilty of "exceptionally grave crimes" as he jailed them for a minimum of 17 years. Ahktar Dogar was told he had robbed a victim known as Girl A of her teenage years. "You took her soul, she felt as though it had been ripped out. You put her parents through years of torture," said the judge.

A second pair of brothers, Bassam Karrar, 33, and Mohammed Karrar, 38, were also given life sentences. Mohammed Karrar was given a minimum tariff of 20 years for the "dreadful offences" he committed against the girls, including one child whom he branded and sold when she was only 11 and forced to have a backstreet abortion when she was 12. The judge said he treated one of his victims as his "commodity" and forced another to carry out "depraved sexual" acts.

His brother Bassam Karrar, who was found guilty of brutally raping and attacking a 14-year-old when high on cocaine, was told that he would serve a minimum of 15 years.

Kamar Jamil, 27, was jailed for life with a minimum term of 12 years. Assad Hussain, 32, and Zeeshan Ahmed, 28, were both jailed for seven years. The men – all from Oxford – were found guilty of 43 charges relating to six victims last month.

The six victims who gave evidence had all been in care and were aged between 11 and 15 when the abuse took place. They were plied with drugs and alcohol, repeatedly raped, sold and trafficked as prostitutes – all at a time during which when they were supposedly in the safekeeping of the local authority. The case comes after high-profile cases in Rochdale, Derby and Telford, where abusers targeted young, vulnerable white girls.

The judge praised the young women who had given evidence said: "Each of these six young girls have shown enormous courage in coming to the Old Bailey to give evidence, knowing they would be accused of lying, knowing they would have to relive their ordeals and knowing they had not been believed in the past ... Their courage has not only exposed your actions but will send the message to others and act as a deterrent to others."

He added that he hoped there would be "lessons learned", adding that he also hoped "the appropriate authorities will not fail to take action" in the future. Years of failings by Thames Valley police and Oxford social services were exposed during the 18-week trial, details of which were so disturbing that jury members were excused from ever having to sit on a jury again. The girls were abused between 2004 and January 2012, but the court heard that police were told about the abuse as early as 2006 and were contacted at least six times by victims.

Despite social workers' fears that the girls were being groomed, no one acted to draw all the evidence together until Simon Morton, then detective chief inspector, took charge of the investigation in late 2010.

Speaking outside the court Morton, who retired last year but continued to lead the investigation, warned abusers that they would be caught. "If you even think about carrying out the sexual atrocities that we have seen in this case, then think again. Look over your shoulder and keep looking over your shoulder. We know how you think, we know how you work. Be under no doubt, we are coming for you."

The police investigation into the Oxford abuse ring is continuing, with more than 50 men contacted about the paedophile ring. Police fear that as many as 50 girls may have been abused.

Baljit Ubhey, chief crown prosecutor for the Thames and Chiltern area, urged other victims to come forward, saying they would be believed.

"[V]ictims who are forced to succumb [...] by the use of such tactics do not, in the eyes of the law, consent to it," she said. The CPS had made child sexual exploitation a priority andhad issued new guidelines, she added.

In a statement, Oxfordshire county council said: "We would like to praise the courage of the victims for giving evidence in court, and we are sorry we did not stop it sooner."

A serious case review has been launched into the failure by authorities to protect the girls.

In the wake of this case, the NSPCC has launched a national programme aimed at combating grooming and sexual exploitation. The Protect and Respect project will target children in schools and in care on how grooming works and what a healthy relationship should be.

Puja Darbari, UK director of policy at Barnardos, said the trial – during which girls were accused by barristers of being "naughty girls" – had exposed failings in the British judicial system.

"Not only have these girls suffered at the hands of their abusers, they have suffered again when they have given evidence," she said.

She welcomed new guidelines from the CPS and Acpos on dealing with vulnerable witnesses, which includes pilots of pre-trial cross examination of witnesses, but said many areas still lacked a vital understand of grooming.

"These moves are making a difference but we still come across agencies who simply don't understand this, and are missing victims. There is still a lot of work to do."