MEXICO CITY (Reuters) - Mexico's government has approved Washington's choice as U.S. ambassador of a Cuban American security expert, as the United States steps up efforts to contain escalating drug violence along its southern border.

Carlos Pascual, a former U.S. ambassador to Ukraine and a senior director on the White House's National Security Council staff, was proposed by President Barack Obama in March.

He was approved by Mexico earlier this month, a Mexican Foreign Ministry spokeswoman said on Monday.

In a short visit to the Mexican capital last week, Obama pledged strong support for Mexico's "courageous" fight against powerful drug cartels whose turf wars killed 6,300 people last year.

Pascual, whose appointment must be ratified by the U.S. Senate, will face the task of helping to stop the flow of guns and drug cash into Mexico from the United States as Mexico grapples with its biggest threat to stability in years.

Armed with huge arsenals, drug gangs fighting over smuggling routes into the United States are taking their feuds into U.S. cities such as Phoenix and increasing their links with U.S. gangs who help distribute narcotics.

The United States is reinforcing security along the U.S.-Mexico border and is sending $1.4 billion in anti-drug aid to give Mexico equipment such as helicopters, as well as funds to clean up corrupt police forces and courts.

Both countries are also looking to resolve a trade dispute over Mexican trucks' access to U.S. roads, part of the North American Free Trade Agreement that Washington has declined to uphold, citing safety concerns.

Mexico has been without an ambassador since Tony Garza ended his term in January after serving under the administration of President George W. Bush.

An expert in conflict management, Pascual was born in Cuba and has urged closer U.S. ties with Latin America. Obama was feted by regional leaders at the three-day Summit of the Americas that ended in Trinidad and Tobago on Sunday.

(Editing by Eric Walsh)