WASHINGTON — Secretary of State John Kerry says the Syrian regime was undermining peace talks that recessed in Geneva without progress last week.

“None of us are surprised that the talks have been hard and that we are at a difficult moment, but we should all agree that the Assad regime’s obstruction has made progress even tougher,” Kerry said Sunday.

While the Syrian opposition offered a road map to a transitional government, “we have seen a refusal to engage on the part of the regime,” Kerry said.

“While it stalled in Geneva, the regime intensified its barbaric assault on its civilian population with barrel bombs and starvation,” he said. “It has even gone as far as to add some of the opposition delegates at Geneva to a terrorist list and seize their assets. This is reprehensible.”

The top U.S. diplomat’s statement was the strongest signal from the Obama administration that the peace talks aimed at removing Bashar al-Assad from power may fail, even as the White House continues to press for a diplomatic solution that avoids U.S. military intervention.

Syrian government and opposition representatives ended a second round of peace talks without agreeing on a date for the next meeting, United Nations mediator Lakhdar Brahimi said Saturday.

Negotiations ended after Assad’s regime refused to discuss a transitional government with an opposition delegation, Brahimi told reporters. The talks began on Jan. 24 under U.N. mediation.

Discussions in Geneva have stalled over an agenda to end the three-year war that’s killed more than 130,000 people. The government insists on tackling terrorism — its term for the opposition — while the rebels want to focus on a transitional government to replace Assad. Brahimi said Assad’s envoys refused to discuss a transitional government.