By Sarah Grainger

GUATEMALA CITY (Reuters) - Secretary of State Hillary Clinton on Friday pledged more U.S. help for Central America's fight against drug cartels, saying the United States was part of the problem as trafficking and violence spread.

"We are going to forge an even closer partnership in the months and years ahead," Clinton told a news conference in Guatemala, the last stop on a five-day Latin America tour.

"We are well aware that Central America is between the countries of Mexico and Colombia that are waging their own very intense efforts against the criminal cartels."

Clinton's stop in Guatemala featured talks with regional leaders on both the drug problem and Honduras, which is struggling to move beyond last year's coup.

Mexico's powerful drug cartels have moved deep into Guatemalan territory in the past few years as a Mexican army crackdown has pushed them to seek new smuggling routes between South America and the United States.

The U.S. Drug Enforcement Administration reckons three-quarters of South American cocaine going north passes through Central America, smuggled by cartels that earn some $40 billion per year.

Clinton said the United States must take some responsibility

for Latin America's drug wars because the huge U.S. domestic drug demand helps to drive the market.

"We know that we're part of the problem," she said. "That's an admission that we have been willing to make this past year and it's one of the reasons why we feel so strongly about trying to help countries like Guatemala fight this terrible criminal scourge."

Traffickers traditionally moved cocaine through Central America by plane or boat but are increasingly developing land-based operations in countries such as Guatemala and Costa Rica, leading to rising rates of local drug violence and addiction.

Central American leaders have complained that their region is increasingly at risk in the drug wars and is not given enough assistance under the 2007 U.S. Merida initiative, which has authorized some $1.12 billion in help since 2008, mostly for Mexico.

"We are convinced that the fight against narco-trafficking and organized crime should be regional," Guatamalan President Alvaro Colom said at the news conference. "We have seen an invasion by the Mexican cartels, we have seen a total invasion of narco-trafficking.

"The cartels move from one place to the next but its our society that is suffering."

Clinton did not provide specifics of the new U.S. help on Friday but has used her visit to reassure Central American governments that they would see more U.S. assistance on things such as maritime security, police and judicial capacity, and anti-corruption efforts.

Guatemala has made several high-profile arrests in recent weeks, including those of the national police chief and anti-drug czar, both charged in connection with the theft of cocaine and guns from a drug gang warehouse last year.

(Writing by Andrew Quinn; editing by Bill Trott)