Officials initially said Umarov himself had surrendered.
A man who identified himself as Umarov's older brother, Akhmad, told reporters he surrendered voluntarily on Friday.
"I have gotten fed up with hiding from authorities and want to return to a normal, peaceful life," he said outside Chechen Prime Minister Ramzan Kadyrov's residence in Gudermes, the second-largest city in Chechnya.
Further details of the incident -- including terms of surrender -- were not available. But authorities last month announced an amnesty for all fighters who turned themselves in. A total of 124 insurgents had turned themselves in under the amnesty as of Saturday, RIA-Novosti reported. Authorities have estimated that Chechen rebel forces number only around 500.
When asked whether he would advise other militants to turn themselves in, Akhmad Umarov said he could not decide for them: "I can't take responsibility for them, and I can't advise them what to do."
While the implications of Akhmad Umarov's surrender were less significant than if Doku Umarov had done so, the move will put more pressure on the rebel leader. Chechen society is highly clan-based, and kinship ties are often considered more sacrosanct than loyalty to government or military unit.
Federal authorities and their Chechen allies have used clan ties in their fight against separatists, detaining or abducting relatives in order to force fighters to give up. The feared Chechen paramilitary run by Kadyrov reportedly detained relatives of Chechnya's late former president and rebel leader Aslan Maskhadov in an attempt to induce him to surrender.
Akhmad Umarov told reporters that he wanted to search for his father, who was kidnapped by unidentified abductors a year ago.
Chechen officials first declared Friday that Umarov himself had surrendered, and later Chechen Interior Ministry spokesman Magomed Deniyev said that it was Umarov's younger brother, Ruslan, who turned himself in. Kadyrov also spoke about Umarov's younger brother who had "actively supported his course."
The web site Kavkaz Center, a rebel mouthpiece, said Doku Umarov did not have a younger brother.
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