The US military has classified the 16-year conflict as a "stalemate" between the struggling US-backed Afghan government and a resurgent Taliban.
Mattis's statement has relevance to India, which has major strategic and economic interests in the Afghan government's stability.
Security situation in Afghanistan worsens
US military: Afghan govt. controls just 60% of nation's territory
A US military assessment found that as of February 20, 2017, the Afghan government controlled or had influence in just 60% of the country's 407 districts. This is a near 11 percentage-point from the same time in 2016.
Mattis says Taliban are "surging," US will counter them
Mattis told the Senate Armed Services Committee: "We are not winning in Afghanistan right now. And we will correct this as soon as possible."
Mattis believes Taliban are currently "surging," an issue he intends to address.
The committee chairman Senator John McCain urged Mattis to consider "a change in strategy, and an increase in resources if we are to turn the situation around."
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Trump reportedly considered sending additional troops, may not yield benefits
In April, it was reported that President Donald Trump was reviewing the situation in Afghanistan and considering sending around 3,000 to 5,000 US and coalition troops there.
Trump considered giving US troops the power to more aggressively engage Taliban fighters.
However, some US officials questioned the benefit of deploying additional troops in Afghanistan, as no politically acceptable number would be enough to create stability.
Why Afghanistan matters to India
India has been among the biggest regional supporters of the current Afghan civilian government and has acted proactively to aid its stability.
Afghanistan is a major bilateral trading partner and India's gateway to trade with Central Asian countries.
India and Afghanistan both victims of Pakistan-sponsored terror
Both the Indian and Afghan government are victims of terrorism and blame the Pakistani government for supporting terror groups. India has worked actively to limit Pakistan's influence in Afghanistan, especially by diplomatically opposing the Islamabad-supported groups like the Taliban.
India's depth of engagement in Afghanistan
India is Afghanistan's fifth largest bilateral donor, and the largest among the non-OECD countries with over $2 billion in development aid as of 2015.
India also has provided approximately $180 million in economic and food aid to Afghanistan.