MEXICO CITY – The United States has written checks for $214 million of the $1.4 billion promised to Mexico in 2007 to help fight the country's powerful drug cartels, Washington's top anti-drug diplomat said on Tuesday.

The amount is a fraction of $1.12 billion authorized by the U.S. Congress since 2008, of which $700 million was part of funds promised under the 2007 Merida Initiative.

The money is intended to pay for equipment and training for Mexican security forces battling the violent drug gangs that send some $40 billion worth of illegal drugs into the United States every year.

A supplemental spending bill signed into law in June included an additional $420 million in aid for Mexico.

We've had some deliveries during the summer of some of the non-intrusive detection equipment that is really at the heart of the material part of this (plan) which provides the sort of technology that is needed so that commerce can be inspected rapidly, U.S. Assistant Secretary of State David Johnson said at a briefing for journalists at the U.S. embassy in Mexico City.

The United States is also helping Mexican police set up internal affairs units to root out corrupt officers and improve recruiting procedures.

Johnson said five Bell helicopters built by Textron Inc worth $50 million are due to be delivered in the fall to the Mexican army.

Mexican President Felipe Calderon has staked his legacy on confronting and crushing the drug cartels that are at the heart of a drug war that has killed more than 13,000 people in the last three years.

The government has poured more than $7 billion into the fight, which has yielded large seizures of drugs and cash but few arrests of top crime lords.

Separately the U.S. and Mexican governments announced an agreement to improve law enforcement communications and the creation of cross-border voice and data transmission networks for police.

(Reporting by Noel Randewich; Writing by Robert Campbell; Editing by Eric Walsh)