Haqqani's brother Serajuddin,himself added to the treasury department's blacklist in 2008, is the commander of the so-called Haqqani network, which is considered the deadliest threat to US and Nato forces in Afghanistan.
According to the treasury, Haqqani functions as an emissary for his brother's network and helps to collect funds from drug trafficking profits and donors in the Arabian Gulf and others connected to al-Qaeda.
Abdullah and Ishakzai have both served as financial specialists for the Afghan Taliban,the treasury said.
Ishakzai, a childhood friend of Taliban founder Mullah Mohammed Omar, heads the group's financial commission and belongs to a council that collects taxes from the Balochistan province in Pakistan.
Quetta, the provincial capital of Balochistan, is believed to be the current headquarters of Omar's movement.
The treasury accused Ishakzai of raising money for suicide attacks and disbursing funds to Taliban fighters and their families.
Abdullah served as a treasurer to Mullah Abdul Ghani Baradar, Omar's deputy, who was arrestedin Pakistan in February. Abdullah has travelled to Kuwait, Saudi Arabia, Libya and the United Arab Emirates to raise money for the Taliban, the treasury said.
While Omar's "Quetta Shura" has shown some interest in negotiating with the Afghan government, the Haqqani network is considered more radical with strong ties to the Pakistani intelligence services.
Some analysts saythat Pakistan is reticent to dismantle the Haqqani network, which is based in the country's restive North Waziristan province, because it views the Haqqanis as a strategic asset against Indian influence in Afghanistan and worries that doing so could trigger a revolt in the northwest tribal areas.
But the United States is wary of the network - nominally led by Serajuddin's father, the ex-mujahideen and reputed former CIA assetJalaluddin Haqqani.
The Haqqani network has been "spearheading insurgent activity" in Afghanistan, according to the treasury department statement.
Shah Mehmood Qureshi, Pakistan's foreign minister, declined to comment directly on the US plan to act against the Haqqanis during Clinton's visit.