A human rights groups says evidence indicates Libyan forces killed at least 17 detainees and arbitrarily executed dozens of civilians as rebels moved into Tripoli.

Human Rights Watch's Middle East and North Africa director says the execution of detainees days before they would have been freed is a “sickening low” in the Libyan government's behavior.

Separately, on August 26, HRW found 18 bodies near a government building near one of Moammar Gadhafi's compounds. The rights groups says witnesses reported Libyan government forces had killed the victims earlier in the week.

HRW said two of the 18 had their hands tied behind their backs, while two more were wearing the green scrubs of Libyan doctors and nurses.

The rights group also found 29 bodies in and around a field clinic where it says “there were signs that Gadhafi loyalists had been present.”

Meanwhile, Libyan rebels said Saturday they have gained control of a key border post near Tunisia, but are still fighting for control of the western city of Zuwarah.

Opposition fighters faced stiff resistance from forces loyal to Mr. Gadhafi during efforts to advance into Zuwarah. A major supply route to Tripoli crosses Zuwarah.

On Friday, rebels seized Ras Adjir, a border post along the same route.

Also Friday, NATO warplanes pounded a large bunker in Mr. Gadhafi's hometown of Sirte. Libya's leader has dropped out of sight since rebel fighters seized Tripoli. Sirte is considered one place where he may be hiding.

Transitional National Council leader Mustafa Abdel Jalil said Saturday that rebels have no “factual” reports on the whereabouts of Mr. Gadhafi or his sons.

U.N. Secretary-General Ban Ki-moon said Friday the international community is ready to send a police force into Libya – if requested – because the country is “awash in small arms.”