Mexico City, May 4 (AFP) The US ambassador to Mexico stepped down today after announcing her resignation in March, setting up a delicate transition period at a time of sharp tension between the two neighbours.

Ambassador Roberta Jacobson was to celebrate a final farewell with embassy staff today afternoon, then fly out on Saturday, the embassy said.

President Donald Trump has not yet named a replacement for the ambassador, a respected Western-hemisphere expert appointed by his predecessor, Barack Obama.

Her deputy, William Duncan, will head the embassy in the interim. The transition comes at a rough moment in US-Mexican relations, as Jacobson herself acknowledged.

"There are differences, there are tensions, we can't deny it," she said Thursday in an interview with Mexican TV network Televisa.

"But that doesn't mean there isn't progress we have to continue in other areas, and also on security and migration." Mexico seethed last month when Trump ordered thousands of National Guard troops to the two countries' border following media reports on a caravan of Central American migrants crossing Mexico toward the United States.

Mexican President Enrique Pena Nieto responded by ordering a sweeping review of Mexico's cooperation with the US, including in the vital areas of security and trade.

Tension has also soared over Trump's vows to build a wall on the border, his disparaging remarks on Mexican immigrants and his threats to axe the North American Free Trade Agreement (NAFTA).

Pena Nieto has twice cancelled plans to visit Washington after heated phone calls in which Trump refused to back off his vows to make Mexico pay for his border wall.

Known as one of the best-liked US ambassadors to Mexico in recent memory, Jacobson sent a series of nostalgic tweets in her final week on her love of Mexico's people, food and natural beauty, and the simple pleasure of walking her dog Taco in the park.

She is one of dozens of senior State Department staff to leave under Trump, who has been slow to fill top diplomatic posts.

Newly sworn in Secretary of State Mike Pompeo vowed Wednesday to work to get the State Department's "swagger back" after the troubled tenure of his predecessor, Rex Tillerson. (AFP) MRJ

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