Blinken, arriving in Kabul after attending NATO talks in Brussels, met with Afghan President Ashraf Ghani, whose government remains embroiled in fierce fighting with Taliban insurgents while a U.S.-backed peace process is shrouded in uncertainty.
The top U.S. diplomat tried to reassure Ghani that despite the departure of U.S. troops, the United States would remain committed to Afghanistan, saying Washington will "intensify" its diplomacy to do "everything we can" to advance efforts to secure a peace agreement between Kabul and the insurgents.
"The reason I'm here, so quickly after the president’s speech last night, is to demonstrate literally, by our presence, that we have an enduring an ongoing commitment to Afghanistan," Blinken said at the embassy, according to a press pool report.
He was in Kabul for about eight hours.
The foreign troop withdrawals have raised concerns that the country could erupt in full-scale civil war, providing al Qaeda space in which to rebuild and plan new attacks on U.S. and other targets.
In his meeting with Ghani at the presidential palace, Blinken assured the Afghan president that "the partnership is changing, but the partnership is enduring."
Later at a press conference at the heavily fortified American embassy, where earlier he had greeted U.S. soldiers, Blinken warned the Taliban that any attack on American troops as they pulled out would be met with "a very forceful response."
Blinken also met with Abdullah Abdullah, the head of Afghanistan's High Council for National Reconciliation, who expressed support for the U.S. decision.
"This does not mean the end of relations and cooperation between the two countries. A new chapter of relations and cooperation between the two countries has returned and we will continue our cooperation in various fields in this chapter," Abdullah said in a statement.
Even as Blinken visited Kabul, the Taliban reiterated a call for an "immediate" withdrawal of all foreign forces, accusing Washington of breaching a February 2020 accord - secured by the Trump administration - to complete a U.S. troop pullout by May 1.
The Taliban statement appeared to make an implicit threat, warning that "in principle" their fighters would "take every necessary countermeasure, hence the American side will be held responsible for all future consequences."
They also said they will "under no circumstance ever relent" on their goal of establishing a "pure Islamic system," underscoring a deep difference with Kabul over the kind of governmental system that should be established in a peace agreement.
As the fate of the peace talks remained uncertain, with the Taliban saying they would not attend a planned conference in Turkey until all foreign forces leave Afghanistan, Blinken remained hopeful.
"We're waiting to see a definitive response form the Taliban about their participation... The goal is ... to accelerate the peace process. The gathering will be supported by high-level attendance from the international community," he said.
Some U.S. officials and experts are concerned about the enduring presence in Afghanistan of al Qaeda and Islamic State extremists, worried that the former will be able to rebuild and plot new attacks on Western targets.
Speaking to CNN, Biden's national security advisor, Jake Sullivan, conceded that the U.S. withdrawal would result in less intelligence. But, he said, the United States still would be able to detect threats to the U.S. homeland from Afghanistan.
"Our ability to protect the American homeland in my view will not diminish," Sullivan said. "Our ability to collect intelligence on a day-to-day basis, against the comings and goings of actors within Afghanistan, will diminish. That's a big difference."
"From our perspective, we can set up the kind of scenario in which we can protect this country without remaining at war in Afghanistan for the third decade."
The Taliban ruled Afghanistan from 1996 to 2001 when they were ousted by U.S.-led forces. A U.S.-backed government has held power in Afghanistan since then, although the Taliban have control over wide areas of the country.
(Reporting by Robin Emmott in Brussels, Charlotte Greenfield in Islamabad and Jonathan Landay in Washington, editing by Sabine Siebold and Nick Macfie) ((firstname.lastname@example.org; +32 2 287 6835; Reuters Messaging: email@example.com))