Peru's new centre-left government is temporarily suspending its modest US-funded coca eradication programme to re-evaluate its strategy.

The prime minister, Salomón Lerner, said the government was committed to reducing the illegal crop and would convene a special panel next month to chart a strategy that would stress alternative development, "social inclusion and fighting poverty".

The government had confirmed the suspension after several newspapers reported it without naming sources.

The US ambassador, Rose Likins, told reporters earlier on her way to see Lerner that she had been surprised by the news.

"It would have been nice to have been informed in advance," she said.

Peru is the world's second biggest producer of cocaine after Colombia. Its area under coca cultivation has grown steadily for four years to reach 61,200 hectares last year, according the UN. Washington gave Peru more than $30m in anti-drugs aid last year.

The president, Ollanta Humala, promised to continue the eradication of the drug in his inaugural address on 28 July, and Lerner said the government was pausing Peru's programme after eradicating two-fifths of its 2011 goal of 10,000 hectares.

That contrasts with the 147,000 hectares that Colombia reported eradicating last year. Bolivia, where the crop is little more than half the size of Peru's and has also been growing, said it had eradicated 8,000 hectares.

Lerner said the pause in eradication was "to refine the instruments necessary for success in the interventions".

A leading Peruvian drug expert, Jaime Antezana, called the announcement bad news for drug-fighters and good news for drug traffickers.

And the former interior minister Fernando Rospigliosi noted in a tweet that the coca crop in the Upper Huallaga valley, the only area where eradication is carried out, had dropped by 25% last year.

"It's not eradication that has failed," he said.

The new head of the state anti-drugs agency, Ricardo Soberón, has been critical of anti-drugs efforts under the previous president, Alan García, saying they were ineffectual across the board. Peru's cocaine seizures under Garcia amounted to less than a tenth of those carried out by Colombia.

Soberon did not specify in a TV interview what changes might be made. The suspension came amid reassignments in the police high command, including the Dirandro anti-drugs unit.

Coca farmers in the Upper Huallaga have complained of being singled out, blocking roads during a weeklong protest last year, and Humala promised to help them during the presidential campaign.

Peru's government does not try to eradicate coca in areas where remnants of the Shining Path rebels operate and where dozens of soldiers have been killed in recent years.