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BRUSSELS (AP) — Gen. David Petraeus, NATO's newly appointed commander of Afghanistan, sought to reassure allies Thursday that the war against the Taliban was going well despite rising military casualties and problems regaining control over key parts of the country.

Petraeus said there would be no change in the counterinsurgency strategy implemented by his predecessor, Gen. Stanley McChrystal, who was ousted last week by President Barack Obama.

But he said the rules of engagement, designed to limit civilian casualties and improve support for U.S. and NATO forces fighting the Taliban-led insurgency, would be examined to improve their efficiency.

"There has been tough fighting and tough casualties ... but we are determined to achieve progress in coming months," Petraeus said.

Petraeus, whose appointment was unanimously confirmed by the U.S. Senate on Wednesday, said the emphasis on reducing civilian casualties would remain a priority.

"In counterinsurgency, the human terrain is the decisive terrain, and you must do everything possible to reduce civilian casualties ... in the course of military operations," he said.

But he added there was no intention of changing the rules of engagement but the alliance would look "very hard at how the rules are implemented and ensure that there is even implementation across all units."

U.S. troops account for two-thirds of the 122,000-strong international force in Afghanistan, while the allies make up the rest.

McChrystal's sacking came amid growing disillusionment with the war in Europe, and a spate of bad news from the battlefields. Allied deaths have doubled in the first six months of this year, with June the deadliest month on record with at least 102 deaths among international service members.

Meanwhile, a widely touted offensive aimed at retaking control of Kandahar, the biggest city in southern Afghanistan, has been repeatedly delayed. An earlier campaign to reassert government control in the market town of Marjah in the southwestern Helmand province, proved inconclusive.

NATO's plans to train and gradually hand over responsibility to the growing Afghan army and police forces has also run into trouble, hobbled by a lack of trainers. A report by the U.S. special inspector general for Afghanistan has found that the ability of Afghan security forces to fight on their own has been overestimated.

The top U.S. general is also the commander of the entire NATO force. Officials said Petraeus would head to Afghanistan immediately after briefing NATO Secretary-General Anders Fogh Rasmussen and envoys from 46 nations taking part in the international force.

"This has been a change of command, not a change of strategy," Fogh Rasmussen told reporters after the meeting. "Gen. Petraeus has our full support."

Some diplomats in NATO have complained that their governments were not consulted by Washington prior to the change of command, even though the allies account for a third of the NATO contingent and nearly 40 percent of the military casualties.

Fogh Rasmussen initially expressed support for McChrystal after the remarks the general made to Rolling Stone magazine, only to backtrack the following day and support Obama's decision to replace him with Petraeus.