WASHINGTON (AFP) - US President Barack Obama Friday gave the Pentagon a year to fix the scourge of sexual assaults that have sparked calls for commanders to lose the power to adjudicate such crimes.

The military in August launched a raft of new measures to combat sexual assaults but their action did not appease some lawmakers who want much stronger measures to deal with hundreds of alleged offenses from harassment to rape.

Mr Obama, who has previously warned that sexual assaults harm military moral and US national security, said in a written statement that he had told Defence Secretary Chuck Hagel and Chairman of the Joint Chiefs of Staff Martin Dempsey to continue efforts to prevent and deal with assaults.

"I have also directed that they report back to me, with a full-scale review of their progress, by December 1, 2014.

"If I do not see the kind of progress I expect, then we will consider additional reforms that may be required to eliminate this crime from our military ranks and protect our brave service members who stand guard for us every day at home and around the world." The Pentagon measures include ensuring legal representation for sexual assault victims at every step of the judicial process, allowing victims to offer testimony at sentencing hearings and providing more scrutiny from the Pentagon's inspector general.

Some lawmakers, however, are urging an overhaul of the military justice system to remove sexual assault cases from the chain of command, as they argue victims remain reluctant to come forward to avoid damaging their career prospects.

Under the current system, commanders decide whether a case should go to trial, who should sit on a jury for a court-martial and can overturn a verdict or revise sentences for those convicted.

Top officers have acknowledged sexual assault cases constitute a crisis in the force but have rejected the idea of rewriting the judicial code as misguided, saying commanders are best placed to attack the problem.

Sexual abuse cases in the military are on the rise, according to a Pentagon report, rising to 3,374 in 2012, a six per cent increase from the previous year.

"So long as our women and men in uniform face the insider threat of sexual assault, we have an urgent obligation to do more to support victims and hold perpetrators accountable for their crimes, as appropriate under the military justice system," Mr Obama said.