U.S. peace envoy Zalmay Khalilzad has called on Afghans to put aside their differences and unite as attempts to end Afghanistan’s 17-year war gain momentum.

Khalilzad has held a series of direct talks with Taliban negotiators in the Middle East in recent months, although those discussions have not included the Western-backed Kabul government.

Key Afghan power brokers who oppose President Ashraf Ghani held talks with Taliban negotiators in Moscow on February 5-6.

Opposition politicians have criticized the negotiating team announced by Ghani that is headed by his chief of staff for not being inclusive.

Khalilzad called on the Afghan government to form a "strong, national" negotiating team.

"We need a team where government’s leadership is respected," Khalilzad told Afghanistan's Tolo News on February 18. "At the same time, the participation of other political elements is also a must."

Khalilzad, a former U.S. ambassador, was in the Afghan capital, Kabul, where he held talks with Ghani and senior political figures.

He said peace would only be achieved in Afghanistan if there was "unity, consensus, and agreement between Afghans, inside and outside the government."

Kabul has been angered and frustrated that it has been left out of the talks.

Ghani said last week he will convene a consultative Loya Jirga, a traditional assembly of tribal, ethnic, and religious leaders, to reach a national consensus on peace talks with the Taliban.

Khalilzad is scheduled to meet Taliban negotiators for talks in Qatar on February 25.

During the previous round of talks in Doha, the Qatari capital, U.S. and Taliban negotiators reached the basic framework of a possible peace deal.

The agreement calls for the Taliban to prevent international terrorist groups from basing themselves in Afghanistan and for the United States to withdraw its forces from the country.

“There are difficulties, but we have agreed with the Taliban to meet again on February 25," he said. "We agreed in principle to talk in details and with more authenticity about two topics to find whether there is the possibility to make more progress on the issue of terrorism and the issue of forces."

The Taliban has yet to make concessions on two key U.S. demands -- implementing a cease-fire and agreeing to negotiate directly with Afghan government representatives as part of an Afghan-led, intra-Afghan peace process.

"I want a broad-based cease-fire to be announced as soon as possible," Khalilzad said. "Secondly, there is a need for discussions and consultations among Afghans, including the [Afghan] government, to start soon."

The Taliban has so far refused to hold talks with Kabul, calling it illegitimate.

The Taliban announced that it would hold talks with U.S. and Pakistani officials in Islamabad on February 18, but the talks were canceled after Kabul's protests.

With reporting by Tolo News and Khaama