U.S. defense officials say the military remains committed to its mission in Afghanistan, despite days of violent protests and attacks on foreign troops that have left close to 40 people dead, including four Americans.

Pentagon officials Monday said members of the U.S.-led coalition are continuing their work training Afghan security forces. The increase in violence, sparked by the reported burning of Qurans on a U.S. military base, has raised questions about the viability of a continued U.S. presence in Afghanistan.

Pentagon spokesman George Little said Defense Secretary Leon Panetta believes the “foundations of our strategy” in Afghanistan remain sound. He said Washington is taking “the long view,” assessing what he said American forces have achieved in reversing the momentum of Taliban insurgents.

Spokesman Little added:

“We will not let recent events allow us to lose sight of the progress we are making toward our broader objectives, including our core goal of defeating al-Qaida and its terrorist allies, and denying it the ability to maintain a safe haven in Afghanistan.”

An American military spokesman in Afghanistan, Navy Captain John Kirby, said that while U.S. troops working with Afghan forces are being more vigilant, that vigilance is not hampering operations. Speaking via video link from Kabul, Kirby said the number of protests has dropped off sharply – from more than 20 a day last week to three on Monday.

Kirby added that a major joint U.S.-Afghan operation, aimed at blocking Taliban insurgents from mounting new attacks as warm weather approaches, wrapped up successfully in southern Afghanistan.

U.S. forces are now watching for possible new attacks on their personnel. On Monday, they were investigating high quantities of chlorine bleach found in coffee and on fruit at a soldiers' dining facility inside a NATO base.

The protests and attacks are in response to news that U.S. troops inadvertently burned copies of the Muslim holy book, the Quran, at the Bagram air base north of Kabul. Media reports say Qurans were being disposed of because of fears that prisoners at the base were using them to pass extremist messages.