Mike O'Connor, a longtime foreign correspondent who had worked in recent years to protect journalists in Mexico, died on Sunday in Mexico City. He was 67.

His death was confirmed by the Committee to Protect Journalists, where he worked as the representative for Mexico. He died from a fatal heart attack while sleeping in his apartment, according to the Los Angeles Times.

Mr. O'Connor had been an outspoken advocate for journalists in Mexico, one of the most dangerous places in the world to be a reporter in the last five years. He challenged government officials to do more to protect journalists and to prosecute their deaths in a country where the crimes often go unpunished.

He understood the rigors of foreign reporting after working in Central America, the former Yugoslavia and Israel for various news organizations, including National Public Radio and The New York Times.

His death will leave a void in the campaign for safety for Mexican journalists, said Javier Garza Ramos, the former editor of the Mexican newspaper El Siglo de Torreon, which was attacked in 2011 by gunfire and a car set on fire. "Mike's presence was essential during a crisis," Mr. Garza Ramos said in a blog post by the Committee to Protect Journalists. "In the rush to take protective measures, Mike's phone calls, several times a day, were not only a reminder that we were not alone, but a guide amid confusion."

Mike O'Connor was born in Germany on Feb. 8, 1946. His father was the director of a large refugee camp there after World War II.

In a 2009 memoir called, "Crisis, Pursued by Disaster, Followed Closely by Catastrophe: A Memoir of Life on the Run," Mr. O'Connor investigated his unusual upbringing in Texas and Mexico, in which his parents sometimes made the family flee their home on short notice without explanation.

Mr. O'Connor started his career in 1983 as a CBS News correspondent covering the wars in El Salvador and Nicaragua. He then covered Central America for National Public Radio and reported from the former Yugoslavia for The New York Times in the 1990s.

He later returned to NPR where he reported from Israel and the Palestinian territories. In 1994, he was part of a team of NPR reporters that won an Overseas Press Award for best radio spot news for a piece on Haiti.