For more than three decades, Pakistan has been home to one of the world's largest refugee communities: the more than one million Afghans who have fled years of warfare in their home country. Living in temporary shelters along the Afghanistan-Pakistan border -- and cared for by the the United Nations High Commissioner for Refugees, Pakistan's government, and numerous international care agencies -- this massive and persistent population remains vulnerable to multiple dangers, from outbreaks of disease to violence spilling over from the war next door. Associated Press photographer Muhammed Muheisen has spent the past several years in Pakistan, documenting the lives of these refugees, with a particular focus on the most vulnerable: the children caught up in the chaos as their families try to keep them safe. Muheisen's portraits below are part of the ongoing series here on Afghanistan.