A top leader of Somalia's Al-Qaeda-affiliated Al-Shabab armed group has surrendered to government and African Union forces and is now in custody, officials said Saturday.

The group’s intelligence chief, Zakariya Ismail Ahmed Hersi, was the subject of a $3 million bounty as part of the U.S. State Department "Rewards for Justice" program. Officials said he surrendered in the Gedo region, where Somalia borders Kenya and Ethiopia.

"Zakariya Ahmed was a very senior person who worked with Godane," said regional military official Jama Muse, referring to former Al-Shabab leader Ahmed Abdi Godane. "He was in charge of intelligence and finances. He was one of the senior Al-Shabab commanders who the Americans put a lot of money on their head."

A U.S. drone strike in Somalia killed Godane in September. The State Department declared Al-Shabab a foreign terrorist organization in 2008, and since then American military forces have targeted the group many times.

An intelligence source said Hersi's surrender was believed to have been motivated by a series of recent bloody splits and purges within the group, with Godane having ruthlessly eliminated many of his rivals and his successor, Ahmad Umar Abu Ubaidah, continuing to maintain strict internal security.

Although presented by the officials as a senior Al-Shabab operative, it was unclear if Hersi had still been active within Al-Shabab in recent months or weeks, or if he was among a large group of commanders who had already fallen out with Godane prior to his death. Some of them were killed in a purge.

There was no immediate comment from Al-Shabab.

The surrender brings some welcome news for Somalia's fragile, internationally backed government as well as the African Union's AMISOM force, who have been facing an almost constant wave of attacks from Al-Shabab despite recent territorial gains in the south and center of the Horn of Africa nation.

The Somali government has also been locked in bitter infighting, with the president this month falling out with his prime minister. According to a Western intelligence source, the surrender could deliver an "intelligence bonanza" that could prove highly damaging to the Al-Qaeda-linked group.

"We're looking at someone who, potentially, will bring with them an encyclopedic knowledge of the organization: Who is in charge of what, what their modus operandi is and so on. It could fill in a lot of intelligence gaps," said the source, who asked not to be identified.

The source also said members of AMISON or the African Union force in Somalia, in particular Kenya, will be urgently trying to recover actionable intelligence on Al-Shabab operations in the border region, the scene of two recent massacres on Kenyan soil carried out by the armed group.

The surrender comes two days after Al-Shabab fighters carried out another high-profile raid in the capital, Mogadishu, where they struck AMISOM's heavily fortified headquarters and killed three soldiers and a civilian contractor.

After the attack, Al-Shabab released a statement vowing that "the mujahideen can and will, by the permission of Allah, strike you anywhere in Somalia."

"What awaits you will be far more grievous and bitter than all preceding attacks. Expect to hear from us again," the group said.

Last year, the group attacked the upscale Westgate mall in Nairobi, Kenya, killing 68 people and injuring nearly 200. Godane said at the time that the attack was in retaliation for a 2011 incursion by Kenyan military forces into Somalia in an attempt to eliminate members of Al-Shabab.

Al Jazeera and wire services