WASHINGTON — The United States on Monday welcomed a Libyan opposition investigation into the assassination of General Abdel Fatah Yunis, chief of the rebel army fighting to oust Moamer Kadhafi.

Libya's National Transitional Council said on Friday it formed a committee to probe the murder of Yunis, whose bullet-riddled and burned body was found in mysterious circumstances in fields just outside the rebel bastion of Benghazi.

"We do welcome the Transitional National Council's move to set up an impartial committee that'll investigate the incident," State Department deputy spokesman Mark Toner told reporters.

"And we look forward to hearing the results," he said.

"It's important that, given the fluidness of the situation on the ground, that the Transitional National Council work to ensure that it takes the right kinds of actions, such as an investigation into the death, that sends a clear and transparent message that they speak on behalf of the Libyan opposition and the Libyan people and that they're diligently carrying out their mandate," he said.

The United States last month recognized the council as the legitimate governing authority in Libya during a transition period that Washington hopes will lead to democracy.

Libyan rebels overnight Sunday rounded up at least 63 people suspected of murdering Yunis, according to rebel representatives.

Rebel spokesman Mahmud Shammam said the group had been rounded up for its role in organizing a prison break in Benghazi last week when about 300 prisoners escaped, including high ranking prisoners of war.

The pro-Kadhafi cell was found in possession of explosives and had "plans to plant car bombs in Benghazi," according to Mustafa Sagazly, deputy chief of the rebel-backed February 17 brigade.

He added the "very same group" -- the Katiba Yussef Shakir -- was suspected in last week's murder of Yunis, a right-hand man to Kadhafi before his defection to rebel ranks.

NTC member Ali Tarhuni has said that those who killed Yunis after he was summoned back to Benghazi from the front by the council for questioning over military issues were members of another shadowy group with suspected Islamist tendencies, Obaidah ibn al-Jarah.