BAGRAM AIR BASE, Afghanistan  Secretive branches of the military’s Special Operations forces have increased counterterrorism missions against some of the most lethal groups in Afghanistan and, because of their success, plan an even bigger expansion next year, according to American commanders.

The commandos, from the Army’s Delta Force and the Navy’s classified Seals units, have had success weakening the network of Sirajuddin Haqqani, the strongest Taliban warrior in eastern Afghanistan, the officers said. Mr. Haqqani’s group has used its bases in neighboring Pakistan to carry out deadly strikes in and around Kabul, the Afghan capital.

Guided by intercepted cellphone communications, the American commandos have also killed some important Taliban operatives in Marja, the most fearsome Taliban stronghold in Helmand Province in the south, the officers said. Marine commanders say they believe that there are some 1,000 fighters holed up in the town.

Although President Obama and his top aides have not publicly discussed these highly classified missions as part of the administration’s revamped strategy for Afghanistan and Pakistan, the counterterrorism operations are expected to increase, along with the deployment of 30,000 more American forces in the next year.