KABUL — The only insurgent leader to sign a peace pact with Afghanistan’s government will return to the country within weeks, his chief negotiator said, in a move that could shake up Afghan politics and complicate the much wider war against the Taliban.

Gulbuddin Hekmatyar, a former warlord who battled US forces after the 2001 invasion and nursed a bitter rivalry with other Afghan factions, agreed to lay down arms last year. Amin Karim, his chief negotiator, said last week that he would return to the capital in ‘‘a matter of weeks, not months.’’

Hekmatyar is seen as a potential rival to President Ashraf Ghani and Chief Executive Abdullah Abdullah, who have governed the country through a shaky, US-brokered power-sharing agreement since the disputed elections of 2014.

His return could inject new political uncertainty as the government struggles to confront a reinvigorated Taliban that has been advancing on several fronts.

The former warlord battled the Soviets in the 1980s and then took part in the civil war that erupted after their withdrawal, clashing with the so-called Northern Alliance, in which Abdullah was a leading figure.

Last year he became the only insurgent leader to sign a peace agreement with the Afghan government, in what many hoped would provide a model for a wider reconciliation with the Taliban.