Mr. Horowitz said he could not confirm that report, but noted that a gas purge last June at a food-processing plant in Garner, N.C., killed four people and injured 67 others.

It aims to raise public awareness around the world about blindness and visual impairment, and to garner support and commitment in ensuring the right to sight for all.

Karzai is still favored to garner the most votes in the first round of voting, but analysts have predicted that the growing challenge from Abdullah and Ghani could force a second round.