"We've been in contact with HTS and with other parties," Blinken told reporters after talks on Syria in the Jordanian Red Sea resort of Aqaba.
He did not give details on how the contact took place but when asked if the United States reached out directly, he said: "Direct contact -- yes."
Blinken said that the contact was partly related to the search for Austin Tice, the US journalist kidnapped in 2012 near the start of the brutal civil war.
"We have pressed upon everyone we've been in contact with the importance of helping find Austin Tice and bringing him home," Blinken said.
He said that in the dialogue with HTS the United States also "shared the principles" on Syria that he has publicly laid out.
Blinken indicated the United States was open eventually to easing sanctions on Syria but not yet.
Referring to HTS statements since their victory, Blinken said: "We appreciate some of the positive words we heard in recent days, but what matters is action – and sustained action.
"This can’t be a decision on the events of one day," he said.
If a transition moves forward, "we in turn will look at various sanctions and other measures that we have taken and respond in kind."
'Inclusive and representative'
Blinken was closing a regional tour in which he has sought common ground after HTS overthrew Bashar al-Assad, whose family ruled brutally for half a century.
In Aqaba, Blinken took part in talks that brought together top Arab and European diplomats as well as Turkey, the main supporter of rebel groups in Syria.
In a joint statement, the participants called for a Syrian-led transition to "produce an inclusive, non-sectarian and representative government formed through a transparent process".
The statement also stressed "respect for human rights", the importance of combating "terrorism and extremism" and demanded "all parties" cease hostilities in Syria.
"Syria finally has the chance to end decades of isolation," the group said.
UN Syria envoy Geir Pedersen earlier told Blinken: "We need to make sure that state institutions do not collapse, and that we get in humanitarian assistance as quickly as possible."
Terrorist designation
The United States and other Western governments classify HTS as a terrorist group due to its roots in Al-Qaeda's Syria branch.
The designation severely impedes activities of businesses and aid workers who risk falling foul of US law enforcement if they are seen as directly supporting a terrorist group.
Since seizing power last weekend, rebel leader Abu Mohammed al-Jolani has spoken in conciliatory terms about making peace with the broad spectrum of Syrian society.
Some analysts note that HTS has not focused on US or other Western targets.
Few expect a quick move by the United States to lift the terrorist designation, especially with a political transition set next month following Donald Trump's victory in the presidential election.
In Britain, a senior minister said that the government would decide quickly whether to remove the terrorist designation but Prime Minister Keir Starmer said it was still "far too early" to do so.
Blinken said that he found hope in the street celebrations in Syrian cities in recent days.
"No one has any illusions about how challenging this time will be, but there's also something incredibly powerful -- the Syrian people determined to break with the past and shape a better future," he said.
He also hailed the US-backed, Kurdish-led Syrian Democratic Forces for raising the new "independence" flag of the rebels, after for years flying their own flag as they achieved limited self-rule.
Blinken said it was for Syrians to decide how to incorporate Kurds in the country but he hailed SDF fighters -- who are bitterly opposed by Turkey -- for their role in fighting the Islamic State group.
