One of Mexico's top police officers has quit after an aide was accused of working for a leading drug cartel, the security ministry said on Saturday, according to Reuters.
Gerardo Garay, acting federal police commissioner, has stepped down and said he will cooperate with an organised crime investigation, a ministry spokesman said.
One of Garay's top lieutenants is being investigated by police on suspicions he was offering protection to the Sinaloa cartel, one of Mexico's main drug gangs.
"I am resigning because in the bloody fight against organized crime. It is our duty to strengthen institutions, which means it is essential to eliminate any shadows of doubt regarding me," Garay said late Friday.
About 4,000 people have been killed in Mexico this year as gangs vie for control of the drug trade and security forces take on the cartels.
Garay's office was allegedly letting the Sinaloa gang move drugs through Mexico City's international airport, Mexican media reported, although the federal Attorney General's office said Garay was not formally under investigation himself.
Mexican authorities have long been dogged by allegations top officials are on the payroll of the cartels that supply Americans with hundreds of tonnes of cocaine every year.
Police recently arrested two top anti-drug officials accused of taking bribes of up to $450,000 (278,000 pounds) a month to leak intelligence to a drug trafficking cartel.
U.S. Customs and Border Protection also arrested a senior Mexican immigration official on the Arizona border last Sunday, accusing him of smuggling marijuana.
Mexican President Felipe Calderon has made cleansing the country's police forces a priority in his fight against drug gangs smuggling narcotics to the United States.
But low wages, shoddy equipment and rising insecurity in the face of the drug war have made that task increasingly difficult.
Calderon has sent more than 40,000 troops across Mexico to fight the drug gangs but despite capturing several drug lords, narco violence continues to spiral out of control.
Security forces recently arrested drug cartel leader Eduardo Arellano Felix, one of the international traffickers most sought by U.S. anti-drug authorities.
Arellano Felix was a senior member of a family cartel of the same name in the violent border city of Tijuana. He faces a five-year old indictment in the United States for drug smuggling.