If the strike was actually carried out by Russia, it could have an effect on talks aimed at ending the Afghan war. Moscow had intended to host those talks on Sept. 4. On Monday, after news of the airstrike, the Russians postponed the talks to an unspecified date, according to Haroon Chakhansuri, a spokesman for President Ashraf Ghani of Afghanistan.

Mr. Chakhansuri said Foreign Minister Sergey V. Lavrov of Russia had called Mr. Ghani and that the two agreed to the postponement. The Taliban had agreed to attend, but the Americans and Afghans had refused.

American officials recently met with Taliban officials in Doha, Qatar, to discuss the possibility of peace talks, an initiative supported by the Afghan government.

[Read about how Afghanistan’s 17-year-long war might end, if it ever does.]

A spokesman for the Taliban, Zabihullah Mujahid, denied in a WhatsApp message that the insurgents had been involved in the Tajikistan border airstrike. He said those killed were smugglers and not part of the Taliban.

The airstrike took place in a heavily forested area that is claimed by both Afghanistan and Tajikistan. The Panj River marks the frontier there, but that river has changed course, leaving the disputed forest on the Tajik side, according to Afghan officials. It is a popular crossing point for smugglers.

On Aug. 13, less than 25 miles from the reported site of Sunday’s attack, a Taliban unit overran an Afghan border police post on the Tajik border at Ay Khanom in Takhar Province, killing 12 police officers and five civilians, according to Afghan officials.

While the Taliban have sanctuaries across the Pakistani border to the east and south, their presence in Afghanistan’s northern neighbor, Tajikistan, is rare. Similarly, cross-border attacks are common along the Pakistan frontier, but they have been rare on the Tajik one.