The Russian Foreign Ministry said on Friday that the United States had told Moscow it would not take part in a conference on Afghanistan in the Russian capital in April, a decision the ministry said it regretted, the Interfax news agency reported.

Moscow is still unaware of the new U.S. administration's stance on Afghanistan, the ministry was cited as saying.

The conference -- the third of its kind in the last five months -- will be held on April 4 and will see participation from 12 countries, including the U.S., China and four Central Asian states.

Pakistan brokered the landmark first round of direct talks between the fragile Afghan government and the Taliban in Islamabad in July 2015; however, the process broke down after the militant group announced the death of their long-term chief Mullah Omer, triggering a bitter power struggle within the militia.

The chance for a resumption of the stalled process dimmed further following the death of Omer's successor, Mullah Mansur in a U.S. drone strike last year on the Pakistani side near the Afghan border.

Since then, several attempts to resume the stalled peace process have been made by a four-nation group comprising Pakistan, Afghanistan, the U.S. and China. Until now, however, these attempts have failed to bear fruit.

Taliban have opened new battle fronts across the war-torn nation in recent months as Afghan security forces -- suffering casualties and desertions -- struggle to beat back a revitalized insurgency.

Recent Taliban successes included the capture of the strategic Sangeen city of the opium-rich Helmand province.

Although U.S.-led coalition forces abandoned their combat mission in Afghanistan in December 2015, they still maintain considerable airpower in the country -- along with 13,000 ground troops -- to support the government's counter-insurgency efforts.