The anti-government group appears to be increasing its strength in the country's northeast.
The Taliban claimed on Saturday that it was in control of Nuristan, a province which adjoins Badakhshan.
The developments come amid accusations by General Stanley McChrystal, the US and Nato commander in Afghanistan, that Iran is training and arming the group.
"The training that we see occurs inside Iran with [Taliban] fighters that move inside Iran, and then the weapons we see come from Iran into Afghanistan," he announced in Kabul, the Afghan capital, on Sunday.
McChrystal did not provide any material to substantiate his assertions, other than saying that the multinational forces that have fought the Taliban fighters for the past eight years have "clear evidence of Iranian activity".
"Iran is a neighbour of Afghanistan and as any neighbour has natural interest inside Afghanistan, and I think in many cases the assistance they provide and the interaction is healthy," he said.
However, Iran's assistance to the Taliban was "inappropriate", he said.
"To the degree that it is inappropriate, we are working to limit what it is now and stop it in the future," McChrystal said.
Iran has in the past repeatedly denied that it supports the Taliban and in turn accused the US of playing a "double game" in Afghanistan.
Afghan officials say they have no evidence that Iran is helping the Taliban.
In another development related to the multinational force in Afghanistan, Brigadier-General Daniel Menard, the chief of Canadian forces operating under Nato, has been dismissed.
Colonel Simon Hetherington, the acting commander, said Lieutenant-General Marc Lessard, commander of Canadian forces abroad, had relieved Menard of his command because of an "alleged inappropriate personal relationship".
Menard has been on leave from Afghanistan for several weeks.
He pleaded guilty on Tuesday at a court-martial in Canada to accidentally firing his weapon at Kandahar Air Field in March and was fined.
The dismissal would not have an impact on the Canadian mission in southern Afghanistan, Hetherington said.
The developments come against a backdrop of increased efforts by the US and Nato military forces to defeat the Taliban by deploying thousands of extra forces.
A major campaign is planned in and around Kandahar city in Afghanistan's south in the coming months.