KABUL, Afghanistan - A top Taliban commander in the midst of peace negotiations with the Afghan government has been detained in the United Arab Emirates, according to Afghan officials, which thwarts long-term reconciliation efforts between insurgents and President Hamid Karzai's government.

Agha Jan Motasim, the Taliban's former finance minister, was taken from his family's home by Emirati authorities about a month ago, Afghan officials said, just as Karzai's government was growing optimistic about a breakthrough in peace talks.

"Known and secret enemies of peace in Afghanistan continue sabotaging our peace process," said Aimal Faizi, a spokesman for Karzai.

Emirati officials declined to comment on Motasim's arrest.

U.S. officials raised doubts about Motasim's role as a prominent peace negotiator, saying his ties to the Taliban leadership had faded in recent years. They added that Motasim's arrest was unrelated to his role as a peace negotiator.

But Afghan officials say Motasim was the best chance Afghanistan had at a peace deal. In recent years, he had held meetings with current and former Taliban members, expressing hope for the peace process. He gave interviews to international media outlets to broadcast his plans for reconciliation.

In the UAE, Afghan officials said, Motasim proved particularly helpful, agreeing to meet with Afghan emissaries in March and attempting to recruit high-level members of the Taliban to the peace process.

But he had long been detached from Taliban leaders - first in Turkey, where he identified himself as an emissary from the organization and then in the UAE. Many Western officials questioned his Taliban bona fides, even as Karzai seemed to invest in Motasim's ability to put an end to the insurgency.

Karzai saw peace with the Taliban as the potential crowning jewel of his presidency. Motasim's arrest is perceived by many in Kabul as making that less likely.