(CNN) -- The commander of Libya's rebel army was killed in Benghazi along with two senior officers on Thursday, rebel leaders announced just hours after claiming big successes on the battlefield.

The death of Gen. Abdul Fattah Younis came after the rebels' Transitional National Council sought Younis for questioning about military matters and alleged ongoing ties to Libyan leader Moammar Gadhafi, according to what Younis' supporters told journalist James Hider of the Times of London.

Supporters also shot at a Benghazi hotel and smashed its windows. Journalists had been gathered at the hotel for a press conference held by the rebel's civilian leader who announced Younis was summoned back to Benghazi and was killed along with his two aides under unclear circumstances, Hider told CNN.

CNN's Ivan Watson analyzes the situation in Libya

Hider described the events surrounding Younis' death as "extremely murky," but he said the rebel army appeared to be on the brink of a rift.

Younis had served as interior minister in Gadhafi's government until February, when he defected to the Benghazi-based rebel movement. He was killed along with a colonel and a lieutenant colonel, the rebels' Transitional National Council said in a statement aired on their television network late Thursday.

No further details were immediately released.

Younis, a onetime general in Gadhafi's army, told CNN in February that he switched sides after Gadhafi told him he planned to have Benghazi bombed -- a move Younis said would have killed thousands.

Rebel forces have been battling to oust Gadhafi since then, aided by a NATO bombing campaign that has targeted government troops under a U.N. mandate to protect civilians. More explosions rocked Tripoli shortly before midnight Thursday (5 p.m. ET), indicating fresh airstrikes were under way in the Libyan capital.

Earlier Thursday, the rebels said their forces had captured five towns and surrounded a sixth in the plains below the Nafusa mountain range, which borders Tunisia.

Hundreds of rebels moved from their mountain positions at dawn. With heavier weapons leading the way with lighter armed fighters following, they initially encountered fierce resistance from Gadhafi's loyalists.

Col. Jumma Ibrahim, spokesman for the Military Council for the western mountain region, said several major battles had taken place before the towns were secured. He named the captured towns as al-Ruwais, Takout, al-Jawsh, Bader and al-Ghazzaya, and the surrounded town as Umm al-Far.

Ibrahim said rebels were now negotiating with Gadhafi troops inside Umm al-Far.

He said four rebels had been killed in the fighting and at least 20 were wounded, while 20 Gadhafi fighters had been captured.

The claimed successes come after one of the biggest rebel offensives in recent weeks and, if true, puts the fighters closer to capturing a significant supply route used by Gadhafi forces.

Ibrahim said that on the eastern side of the mountains, Gadhafi forces had been shelling rebel-held positions near Beir al-Ghanam and also near Qawalish.

Rebel fighters last month suffered heavy casualties in a failed attempt to wrest control of al-Ghazzaya from forces loyal to Gadhafi.

Last week, rebel fighters manning hilltops in the western mountains overlooking al-Ghazzaya told CNN that they had been watching the government forces reinforcing their weapon stocks with heavy military machinery and rocket launchers.

The United Kingdom on Wednesday recognized the Benghazi-based rebels as Libya's legitimate government, and the United States recently recognized the council as the country's "legitimate governing authority."

British Foreign Secretary William Hague on Wednesday reiterated his stance that Gadhafi could remain in Libya if he leaves power, but added that the best thing would be for him to face justice at the International Criminal Court, which is seeking his arrest.

CNN's Michael Martinez contributed to this report.