Zalmay Khalilzad left Sunday on a journey that will run through May 11 and take him both to Afghanistan and Qatar, the usual venue for talks with the Taliban.

In the Qatari capital Doha, "he will continue to press forward on negotiations with the Taliban to reach a consensus on core national security issues, and urge their participation in an inclusive intra-Afghan dialogue," a State Department statement said, without directly confirming he would meet again with the Taliban.

Despite several rounds of talks with Khalilzad, the Taliban have refused to negotiate with Afghan President Ashraf Ghani's internationally recognized government.

Hopes for a breakthrough last weekend were dashed when a dialogue planned between the Taliban and Afghan officials in Doha collapsed at the last minute.

Ghani had announced a delegation of some 250 people from all walks of Afghan life, including government figures, but the Taliban rejected the lengthy list, saying the meeting was "not an invitation to some wedding or other party at a hotel in Kabul."

Secretary of State Mike Pompeo voiced disappointment over the impasse during a call on Saturday with Ghani.

Pompeo "encouraged all sides to seize the moment and reach an understanding on participants, so that an inclusive intra-Afghan dialogue can be convened in Doha as soon as possible," State Department spokeswoman Morgan Ortagus said.

President Donald Trump is eager to reach a solution to end the longest-ever US war, which dislodged the Taliban following the September 11, 2001 attacks.

The Taliban's political spokesman Suhail Shaheen told AFP that the upcoming talks would focus on a timetable for pulling all foreign forces from Afghanistan.

Khalilzad on his trip will also visit four other countries with deep interests in Afghanistan -- Pakistan, India, Russia and Britain.