Khalilzad was to leave the United States on Tuesday for Doha, and after talks there he will travel to Kabul to consult with the Afghan government on the peace process.

His discussions with the Afghan leadership will "encourage full preparation for intra-Afghan negotiations," the department said.

Khalilzad, the US special representative for Afghanistan reconciliation, bolstered optimism for a peace agreement last week when he concluded the eighth round of negotiations with the Islamist insurgents with a tweet saying he hoped this is the final year that the country is at war.

The talks aim at ending the 18-year US involvement in the country and beginning the return of the 14,000 US troops based there.

On Tuesday morning Secretary of State Mike Pompeo told CNBC television that a deal was possible, if the current level of violence in the country can be significantly reduced.

"The conversations are going well," Pompeo said.

"What really happens on the ground, if we can reduce violence, we'll create a space where we can withdraw not only American support but NATO forces that are there as well."