Scuffles, vandalism and angry accusations by supporters of Mexico's two presidential rivals brought the capital nearly to a boiling point, as politicians appealed for calm to prevent the election dispute from erupting into violence.
Leftist Andres Manuel Lopez Obrador has called on his backers to mount a civil resistance campaign against what they claim is vote fraud that helped his conservative Felipe Calderon win the July 2 vote.
Calderon was harassed on Tuesday by a knot of leftists who banged on his car and screamed "pig" at him. In turn, the conservative and his staff on Wednesday touted support from a purported union "leader" who doesn't appear to hold any post.
Calderon's staff introduced Gaston Saenz as a top adviser of the Electrical Workers Union, and stood by smiling as Saenz pronounced the election clean.
But union chief of staff Enrique Bernal later said Saenz was a retired member of the union, and that he currently held no post and did not speak for the group.
Calderon's campaign did not issue a formal response to the union's claim and a spokeswoman was not immediately available for further comment.
Earlier on Wednesday a pro-Lopez Obrador art display was vandalized at a downtown park, and local media reported that cars bearing bumper stickers in favor of both candidates had been vandalized. A group of pro-Lopez Obrador protesters also briefly blocked a Banamex bank branch in the capital's historic downtown.
"We shouldn't get into a situation of violence," said Enrique Cuevas, the host of a news program for the Formato 21 radio station. "We are falling to a low political level that isn't going to lead us anywhere."
An official tally gave Calderon a 244,000-vote advantage, a margin of less than 0.6 percent of the total vote in the July 2 race. Lopez Obrador has challenged the lead in Mexico's top electoral court, which must rule on appeals by Aug. 31 and declare a president-elect by Sept. 6.