WASHINGTON—A fresh contingent of Marines arrived in Kabul on Saturday as part of a 3,000-troop force intended to secure an airlift of U.S. Embassy personnel and Afghan allies as Taliban insurgents approach the outskirts of the capital. The last-minute decision to re-insert thousands of U.S. troops into Afghanistan reflects the dire state of security and calls into question whether President Joe Biden will meet his Aug. 31 deadline for fully withdrawing combat forces. After an advance group of Marines arrived on Friday, more flowed into the Kabul international airport on Saturday, said Navy Capt. William Urban, a spokesman for U.S. Central Command. Citing operational security, Urban declined to provide specific numbers. The Pentagon said on Friday that the bulk of the 3,000—comprising two battalions of Marines and one of Army soldiers—are due by the end of the weekend. Officials have stressed that the newly arriving troops’ mission is limited to …