By Alizeh Kohari

MEXICO CITY, Aug 2 (Reuters) - Mexico's largest airline group, Aeromexico, will increase the frequency of flights on five of its main international routes, the company said on Tuesday.

On its European routes, Aeromexico will offer daily flights from Mexico City to Amsterdam and to London Heathrow - up from three and six flights per week, respectively. The carrier will increase its seat capacity to Madrid by 15 percent, for a total of 12 flights per week.

Aeromexico also plans to increase its service to Asian destinations such as Shanghai by more than 65 percent. In South America, daily service to Santiago, Chile, will be added.

The move contrasts with the biggest U.S. airlines, which have been slowing growth plans for after the peak summer travel season.

Aeromexico code-sharing partner Delta Air Lines Inc, for example, plans to cut back flights between the United States and United Kingdom this winter. The reductions highlight the threat that Britain's planned exit from the European Union and new airline competition pose to U.S. airlines, which have raked in cash from trans-Atlantic flights.

Aeromexico's changes follow a new air transportation agreement between the United States and Mexico that is expected to boost travel and clear the way for any city to have direct airline service to the neighboring nation.

In May, Aeromexico started direct service from Mexico City to Amsterdam, and since the second quarter of last year, it has launched international routes from Mexico City to Panama, Toronto, Boston, Vancouver and Santo Domingo.

Delta is forming a joint venture with Aeromexico and plans to own up to 49 percent of the Mexican carrier by year-end.

(Reporting by Alizeh Kohari; Editing by Christian Plumb and Leslie Adler)