Former senior U.S. officials have urged the U.S. secretaries of state and defense to do more to provide visas to Afghans who worked for the United States in Afghanistan before U.S. forces withdraw, according to letters seen by Reuters on Wednesday. President Joe Biden has decided to withdraw all U.S. troops from Afghanistan by Sept. 11, raising concerns of a full-scale civil war, the Taliban"s return to power and continued reprisals against Afghans associated with the U.S. presence. "U.S. history is replete with instances where we failed to understand or prepare to mitigate the terrible consequences that might confront those ... who stood beside us and believed in us when the going was tough," said the letters to Secretary of State Antony Blinken and Defense Secretary Lloyd Austin. "We have a moral obligation to do better this time," they added. The letters were signed by nearly 100 former officials, including many who worked on U.S. policy toward Afghanistan in the 20 years since the U.S. military helped topple the Taliban government that harbored al Qaeda leaders blamed for the Sept. 11, 2001, attacks on the United States. The officials - who included four former U.S. ambassadors to Afghanistan and retired General Joseph Votel, who oversaw U.S. troops in the Middle East - called on the Biden administration speed up the processing of so-called Special Immigrant Visas (SIV) for Afghans who worked for the United States. The letter said more than 18,000 Afghans, including former interpreters, are awaiting visa adjudication and said the U.S. should aim to clear the backlog before U.S. troops withdraw. They also proposed increasing quotas when U.S. troops pull out and asking Congress to create a pathway to admit "additional Afghans who will be especially vulnerable in the post-withdrawal period." The State and Defense Departments did not immediately respond to a request for comment.