The United States said on Tuesday that one of many concerns about Afghanistan is that it could spiral into civil war.
Since the United States announced plans in April to withdraw its troops with no conditions by Sept. 11 after nearly 20 years of conflict, violence has escalated throughout the country as the Taliban seeks more territory.
Peace talks between the Afghan government and Taliban negotiators started last year in the Qatari capital of Doha, but have not made any substantive progress. US State Department spokesman Ned Price said the Taliban saw "the utility of a negotiated solution, they are engaged in Doha."
"If they seek to contravene what they have said, then they will be an international pariah ... and the concern on the part of all of us, one of the many concerns is that the result will be a civil war," Price told reporters.
The Taliban and the Afghan government are far apart in the Doha talks, with the insurgents demanding "the lion's share of power" in any new government, US special envoy Zalmay Khalilzad said earlier on Tuesday.
A car bomb blast followed by sporadic gunfire hit Afghanistan's capital Kabul on Tuesday near the heavily fortified "Green Zone," leaving three civilians and three attackers dead, security officials said.
"It does bear all the hallmarks of the spate of Taliban attacks that we have seen in recent weeks," Price said. "We unequivocally condemn the bombing."
In a statement on Tuesday condemning an attack on the United Nations in Afghanistan last week, the UN Security Council also "expressed their deep concern about the high levels of violence in Afghanistan following the Taliban's military offensive, and called for an immediate reduction of violence."
The council called on the Taliban and the Afghan government to "engage meaningfully in an inclusive, Afghan-led and Afghan-owned peace process."