(CNN) Taliban leader Mullah Mohammed Omar died in April 2013 in Pakistan, a spokesperson for Afghan President Ashraf Ghani said Wednesday in a news release, citing "credible information."

Under Omar's leadership, the Taliban offered safe haven to al Qaeda leader Osama bin Laden, precipitating the U.S. military action in Afghanistan after the terror attacks of September 11, 2001.

White House deputy press secretary Eric Schultz could not confirm the death but said the administration believes the reports are credible. Schultz says the intelligence community is looking into the reports.

Haseeb Sediqi, spokesman for Afghanistan's intelligence service, said Omar died in a hospital in Karachi, Pakistan, in April 2013.

Sediqi said that intelligence service -- the National Directorate of Security -- was aware of Omar's death long ago and had conveyed that to Afghanistan's Parliament. He also said he mentioned it at least three times in his past press conferences.

Omar Samad, senior adviser to Afghan Chief Executive Abdullah Abdullah, said, "All odds and indications point to the fact that he has been dead for at least two years,"

A source with a strong decades long track record of contact with the Taliban told CNN that senior Afghan Taliban leadership have acknowledged Omar is dead. They met in Quetta, Pakistan, this past weekend and may take days or longer to acknowledge his passing publicly, the source said.

The source said there are at least two versions of the death: That Omar died at a Karachi hospital or in the Afghan village of his birth.

Peace talks

Omar's apparent death is seen as enhancing the possibility of a positive outcome of talks between the Afghan government and the Taliban, the source said.

A former senior United States government official who worked on Afghanistan issues for many years weighed in on the significance of Omar's death.

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"I've tended to believe the rumors that he was dead since the serious splits started in the Taliban," the official said.

"If he were alive, he wouldn't allow these rumors to continue to threaten the movement's unity to this degree. He would risk some small exposure to invalidate the rumors, and he has not done that despite incredible internal demands that he do so."

Samad said the reports of Omar's death will complicate the Afghan government's negotiations with the Taliban

"There is a serious ongoing power struggle that will now become more apparent between his hard-line followers and those who are more amenable to current reconciliation initiatives facilitated by Pakistan," he said, referring to peace talks between the Afghan government and the Taliban that were hosted in Pakistan this month.

In announcing Omar's death, the spokesman for Ghani said the government is optimistic about the talks, "and thus calls on all armed opposition groups to seize the opportunity and join the peace process."

ISIS to benefit?

Omar's death will likely work to the advantage of ISIS, which is seeking to make inroads among the Afghan Taliban and the Pakistani Taliban.

Photos: The Taliban Photos: The Taliban The Taliban, a Sunni Islamist organization operating primarily in Afghanistan and Pakistan, was formed in 1994. It was led by Mullah Mohammed Omar, a veteran of the Afghan mujahedeen that fought invading Soviets from 1979-1989. Omar, seen here in an undated video image, died in April 2013 , according to a representative for Afghan President Ashraf Ghani. Hide Caption 1 of 16 Photos: The Taliban In this image taken off television by BBC Newsnight, Omar -- fourth from left -- attends a rally with Taliban troops before their victorious assault on Afghanistan's capital, Kabul, in 1996. The Taliban's aim is to impose its interpretation of Islamic law on Afghanistan and remove foreign influence from the country. Most of its members are Pashtun, the largest ethnic group in Afghanistan. Hide Caption 2 of 16 Photos: The Taliban Tanks manned by Taliban fighters are decorated with flowers in front of the presidential palace in Kabul on September 27, 1996. Hide Caption 3 of 16 Photos: The Taliban Taliban soldiers in Russian-made tanks fire on the forces of former Afghan defense minister Ahmad Shah Massood in October 1996. Hide Caption 4 of 16 Photos: The Taliban Afghan women in Kabul are covered head to toe in traditional burqas on October 16, 1996. After taking over Kabul, the ruling Taliban imposed strict Islamic laws on the Afghan people. Television, music and non-Islamic holidays were banned. Women were not allowed to attend school or work outside the home, and they were forbidden to travel alone. Hide Caption 5 of 16 Photos: The Taliban Three women hitch a ride on the back of a donkey cart as they pass by the ruins of Kabul's former commercial district in November 1996. Hide Caption 6 of 16 Photos: The Taliban This is an undated image believed to show the Taliban's former leader, Mullah Mohammed Omar. In 1997, the Taliban issued an edict renaming Afghanistan the Islamic Emirate of Afghanistan. The country was only officially recognized by three countries: Pakistan, Saudi Arabia and the United Arab Emirates. Hide Caption 7 of 16 Photos: The Taliban In 1997, Omar forged a relationship with al Qaeda leader Osama bin Laden, pictured. Bin Laden then moved his base of operations to Kandahar, Afghanistan. Hide Caption 8 of 16 Photos: The Taliban In March 2001, Taliban soldiers stand at the base of the mountain alcove where a Buddha statue once stood 170 feet high in Bamiyan, Afghanistan. The Taliban destroyed two 1,500-year-old Buddha figures in the town, saying they were idols that violated Islam. Hide Caption 9 of 16 Photos: The Taliban After the 9/11 attacks, the United States conducted military strikes against al Qaeda training camps and military installations of the Taliban regime. In this long-exposure photo, a U.S. Navy fighter jet takes off from the deck of the USS Enterprise on October 7, 2001. Hide Caption 10 of 16 Photos: The Taliban An Afghan anti-Taliban fighter pops up from his tank to spot a U.S. warplane bombing al Qaeda fighters in the Tora Bora region of Afghanistan on December 10, 2001. After massive U.S. bombardment as a part of Operation Enduring Freedom, the Taliban lost Afghanistan to U.S. and Northern Alliance forces. Hide Caption 11 of 16 Photos: The Taliban Afghans look into Omar's bedroom as they go through his compound on the outskirts of Kandahar on December 11, 2001. Hide Caption 12 of 16 Photos: The Taliban In April 2011, hundreds of prisoners escaped from a prison in Kandahar by crawling through a tunnel. The Taliban took responsibility for the escape. This picture shows a general view of the prison, top center, and the house, bottom right, from which Taliban militiamen dug the tunnel leading to the prison. Hide Caption 13 of 16 Photos: The Taliban Security guards stand outside the new Taliban political office in Doha, Qatar, before its official opening in June 2013. The Taliban announced that they hoped to improve relations with other countries, head toward a peaceful solution to the Afghanistan occupation and establish an independent Islamic system in the country. Hide Caption 14 of 16 Photos: The Taliban Zafar Hashemi, deputy spokesman for Afghan President Ashraf Ghani, speaks during a news conference on July 29, when the news of Omar's death was announced. Hide Caption 15 of 16 Photos: The Taliban Mullah Akhtar Mohammad Mansour became the leader of the Taliban after Omar's death. Mansour was killed in an airstrike in Pakistan on Saturday, May 21, 2016 Hide Caption 16 of 16

"Some dissatisfied elements (of the Taliban) have already pledged allegiance to (ISIS)," said Samad. "With Omar out of the equation, more are likely to join (ISIS)."

"The bad news is that the hardline faction would then become relatively independent, perhaps even aligning with ISIS, which is a nightmare scenario for us," the senior U.S. official said.

The BBC and the Wall Street Journal reported earlier Wednesday that unnamed sources in Afghanistan were saying Omar was dead. His death had long been rumored, yet always dismissed by the Taliban. Twice in 2011, the Taliban denied speculation that he had been killed.

Earlier this year, the Taliban published a "biography" of the reclusive Afghan leader, saying he was still in charge. The piece appeared on a Taliban website. The goal of the biography, experts said, was to dispel rumors that he died, possibly years ago.

And just two weeks ago, the Taliban released a statement attributed to Omar, saying he backed peace talks between the Taliban and the Afghan government.

However the Taliban released a statement Thursday that seemed to contradict this. It read: "Media outlets are circulating reports that peace talks will take place very soon between the Islamic Emirate (as the Taliban refers to itself) and the Kabul regime either in the country of China or Pakistan.

"The Islamic Emirate has handed all agency powers in this regard to its Political Office and they are not aware of any such process.

"The Islamic Emirate, in accordance with its policy, has established a specific organ responsible for handling all its political affairs. We have repeatedly clarified this matter before and made clear the stance of Islamic Emirate."

Swept to power

Omar, once a rural Islamic cleric, created the Taliban -- the plural of the Pashto word for "student" -- in the 1990s in the wake of the Soviet Union's withdrawal from the country, aiming to impose Islamic law on Afghanistan and remove foreign influence from the country. The Taliban eventually swept across the nation.

With most of the country under Taliban control, he set himself the goal of transforming Afghanistan into the purest Islamic state in the world, declaring himself Amir-ul-Momineen, or head of the Muslims.

He was Afghanistan's de facto leader from 1996 until late 2001, when a U.S.-led coalition invaded and booted the Taliban from power for refusing to hand over Osama bin Laden after the 9/11 terror attacks.

That led to a Taliban insurgency that continues to this day, even as U.S. and other NATO troops are drawing down their numbers in Afghanistan.

The U.S. combat mission in Afghanistan ended last year, leaving the Afghan military to lead the fight against the Taliban. The thousands of NATO troops that remain in Afghanistan are there in a training and support role.