WASHINGTON, July 21 (Reuters) - Taliban insurgents control about half of Afghanistan's district centers, the senior U.S. general said on Wednesday, indicating a rapidly deteriorating security situation.

Insecurity has been growing in Afghanistan in recent weeks, largely spurred by fighting in its provinces as U.S.-led foreign troops complete their withdrawal and the Taliban launch major offensives, taking districts and border crossings.

"Strategic momentum appears to be sort of with the Taliban," General Mark Milley, the chairman of the Joint Chiefs of Staff, told reporters.

Milley said more than 200 of the 419 district centers were under Taliban control. Last month, he had said the Taliban controlled 81 district centers in Afghanistan.

While the insurgent group had not taken over any provincial capitals, they were putting pressure on the outskirts of half of them, he said.

The government has accused the Taliban of destroying hundreds of government buildings in 29 of the country's 34 provinces. The Taliban deny accusations of extensive destruction by their fighters.

Fifteen diplomatic missions and the NATO representative in Afghanistan urged the Taliban on Monday to halt its offensives just hours after the rival Afghan sides failed to agree on a ceasefire at a peace meeting in Doha.

Biden has set a formal end to the U.S. military mission in Afghanistan for Aug. 31 as he looks to disengage from a conflict that began after al Qaeda's attacks on the United States on Sept. 11, 2001.

Almost all U.S. troops, except those protecting the embassy in Kabul and airport, have left the country.