ISLAMABAD — A key gathering was underway Monday in Islamabad with four countries — Afghanistan, Pakistan, China and the United States — hoping to lay the roadmap to peace for the war-shattered Afghan nation.

The meeting comes as Afghanistan’s battlefield losses are mounting and some parts of the country are under constant threat from Taliban gunmen. Taliban representatives have not been invited to the talks, vowing to talk only to the U.S. and not to the government in Kabul.

As the gathering got under way, host Pakistan — seen as key to bringing the warring Taliban factions to the table — cautioned of the difficulties ahead.

Sartaj Aziz, adviser to the Pakistani prime minister on foreign affairs, warned against prematurely deciding which Taliban factions are ready to talk, urging instead “confidence building” measures to get even the recalcitrant Taliban to the negotiating table.

But analysts and participants say much of the hope for progress toward peace rests with Pakistan, which is accused of harboring some of the fiercest factions of the Taliban, including the Haqqani group, a U.S.-declared terrorist organization. Pakistan says its influence over the Taliban is overrated.