(Adds detail from Michoacan in paragraphs 10 and 11)

By Dave Graham

MEXICO CITY, Feb 13 (Reuters) - A U.S. decision to suspend avocado shipments from a violent Mexican state sealed a challenging week for President Andres Manuel Lopez Obrador, whose approval rating suffered an unusual dip in a tracking poll published on Sunday.

Lopez Obrador, whose still robust popularity has been more resilient than most global leaders, has this month become embroiled in a war of words with a critical journalist over his reporting on the lifestyle of one of the president's sons.

On Friday, the president devoted a chunk of his daily news conference to criticizing journalist Carlos Loret de Mola - and named his salary - just a day after authorities had confirmed the fifth killing of a media professional in Mexico this year.

"He's gone from being against the system to 'I am the system'," said Roy Campos, head of polling firm Consulta Mitofsky, whose tracking poll this weekend showed support for Lopez Obrador taking its biggest daily drop in nearly two years.

The poll published on Sunday shows the left-leaning Lopez Obrador with an approval rating of 61.2%, 0.6 percentage points lower than on Saturday and 1.5 points lower than a week earlier.

Lopez Obrador argues that Loret is part of entrenched interests resisting his project of making Mexico a fairer society. But his singling out of the journalist at a time of heightened sensitivity about the profession has stirred unease.

Loret said the revelations have put him in danger, and that Lopez Obrador was angry because his reporting on the son's apparently expensive lifestyle sat awkwardly with the image of personal austerity the president has projected.

On Saturday, without mentioning Loret, the U.S. embassy in Mexico said it was "dismayed" https://www.reuters.com/article/us-mexico-violence-usa/u-s-embassy-dismayed-over-violence-against-journalists-in-mexico-idUSKBN2KH0OG by the situation journalists faced in the country, pointing to the latest killing.

Later in the day, the Mexican government said the United States had temporarily suspended https://www.reuters.com/article/mexico-usa-avocado/mexico-says-u-s-suspends-avocado-shipments-from-michoacan-state-idUSKBN2KI00M avocado shipments on security grounds from the western state of Michoacan, the country's top producing region, which has long been plagued by gang violence.

The U.S. embassy said the U.S. avocado inspection program in Michoacan had been suspended pending a review of the security situation. Though exports are not "blocked", U.S. officials must inspect all avocados being sent to the United States, it noted.