Peru's government on Tuesday replaced its drug czar, whose refusal to endorse an all-out coca crop eradication effort put him at odds with the Cabinet chief and prompted concern by the U.S. Embassy.
Ricardo Soberon's resignation came after just five months in office.
He caused a stir in August by temporarily suspending manual eradication of Peru's coca crop, the world's second largest after Colombia's.
The move surprised U.S. Ambassador Rose Likins, she said at the time. Her government pays for Peru's eradication program and considers it integral to combatting the illegal drugs trade.
The interior minister at the time, Oscar Valdes, disagreed with the suspension, which ran counter to an inaugural pledge by President Ollanta Humala. Valdes became Cabinet chief in December.
"Soberon's exit was a matter of time," drug policy expert Jaime Antezana said. "There was no chance that Oscar Valdes would keep him in the job."
Phone calls to Soberon seeking comment were not returned.
He has argued that Peru should vigorously pursue cocaine traffickers and money launderers, seizing illegal drug shipments and halting the influx of chemicals used to process cocaine, but put less emphasis on penalizing peasants who grow coca, the raw material of cocaine.
"I think that was the difference in practice over which they (Soberon and Valdes) couldn't come to agreement," Tulio Mora, a Soberon adviser, told The Associated Press.
Soberon's national drug strategy plan was never approved.
His departure was widely seen as the latest sign Humala, who has also backed a controversial major gold mining project, has veered from the leftist agenda on which he initially campaigned before winning a June runoff.
Prior to his election, Humala told coca growers he would not aggresively pursue eradication. Soberon had worked closely for years with many coca growers and sent the same message.
Drug policy expert Kathryn Ledebur of the Bolivia-based Andean Information Network said Soberon's resignation could raise the potential for violence in Peru's coca-growing regions.
"With Soberon's appointment, for the first time in Peru you had a drug control chief with legitimacy with the affected coca-grower population," she said.
Hopes for a Bolivian-style approach to eradication that is less alienating to growers are now dimmed, she added.
Bolivia is the world's No. 3 cocaine source and its leftist president and longtime coca-growers' leader, Evo Morales, expelled the U.S. Drug Enforcement Administration in 2008, accusing it of inciting his political opponents.
The U.S. Embassy in Lima had no comment on Soberon's resignation, spokesman James Fennell said.
U.S. officials have expressed worry over Peru's coca crop, which continues to grow steadily while that of Bolivia, half the size of the Peruvian crop, increased by just 0.3 percent in 2010, according to the United Nations.
Rodney Benson, DEA chief of intelligence, told a U.S. congressional hearing in October that "although Colombia remains the world's largest cultivator of coca, for the first time in over a decade, the U.S. government estimates that Peru has surpassed Colombia in potential pure cocaine production."
He said Peru's higher-yielding mature coca fields enabled the country to potentially produce 325 metric tons of pure cocaine, compared to only 270 metric tons in Colombia, putting Peru's production levels at their highest since 1995.
According to U.N. figures, Peru had 61,200 hectares (236 square miles) under coca cultivation in 2010, just 800 hectares (three square miles) fewer than Colombia.
Peru met its eradication target of just over 10,000 hectares (39 square miles) of coca plants last year, but its drug seizures were down in the second half of 2011 to 7 percent of estimated production from 10 percent in the first half of the year, Mora said.
Soberon was replaced by Carmen Masias, a psychologist by training who has consulted for the U.S. Agency for International Development.
Asked about eradication policy at a news conference on Tuesday with Valdes, Masias referred questions on the subject to the Interior Ministry, saying it is in charge of that realm.
Unlike Colombia's cocaine, most of which ends up in the United States, Peru's output primarily supplies Europe as well as a growing Asian market.
Associated Press writer Martin Villena contributed to this report.