(Lefteris Pitarakis | AP) Protester gather during a demonstration against the killing of Iranian Revolutionary Guard Gen. Qassem Soleimani, seen in posters, close to United States' consulate in Istanbul, Sunday, Jan. 5, 2020. Iran has vowed "harsh retaliation" for the U.S. airstrike near Baghdad's airport that killed Soleimani, as tensions soar in the wake of the targeted killing.