WASHINGTON (AP) — Just hours after the U.S. military launched an airstrike targeting Taliban fighters in Afghanistan, top defense leaders told Congress that the results of the peace deal signed on Saturday have been mixed, but the insurgent group is abiding by much of the accord.

The American airstrike was triggered by a spike in violence by the Taliban against members of the Afghan security forces.

The exchange of violence came not long after President Donald Trump described what he called a “very good talk" with a Taliban leader on Tuesday, and insisted the group wants to cease violence. It underscored the fragility of the U.S.-Taliban peace accord and the murky nature of what the U.S. may or may not do to try to enforce or encourage it.

Defense Secretary Mark Esper told a Senate panel Wednesday that the Taliban are honoring the agreement by not attacking U.S. and coalition forces, “but not in terms of sustaining the reduction in violence.” He added that, “keeping that group of people on board is a challenge. They've got their range of hard-liners and soft-liners and so they’re wrestling with that too, I think..”

Other U.S. officials said Wednesday's airstrike was meant to send a message to the Taliban that the increased attacks against the Afghans over the last two days was unacceptable.

Esper, who was in Kabul on Saturday with Afghan leaders while the peace agreement was signed in Doha, said the document allows the U.S. to act in defense of the Afghan forces. “It’s the commitment I made to the Afghans when I was there on Saturday. We would continue to defend the Afghans,” he said.

The peace deal calls for a comprehensive nationwide cease-fire to be negotiated in talks between Afghans on both sides of the conflict, and it says the U.S. must begin withdrawing more than 4,000 U.S. troops from Afghanistan in the next week or so. It does not, however, say that the truce or completion of a peace accord are required conditions for the American withdrawal.

Instead, the agreement signed in Doha says the phased drawdown of U.S. and allied troops is dependent on the Taliban entering those negotiations and taking them seriously, and requires that the insurgent group meet its counterterrorism commitments, including a rejection of al-Qaida and other groups.

Officials agree that fueling the increased Taliban violence is the Afghan government’s refusal thus far to agree to release thousands of Taliban prisoners ahead of the all-Afghan talks that are supposed to begin next week. And officials insist that the burst of violence would not necessarily crater the agreement and that they had always expected implementation would face challenges. The officials spoke on condition of anonymity to discuss internal deliberations about the agreement.

Although the “reduction in violence” agreement that had preceded Saturday’s signing ceremony had been expected to be respected in the meantime, the U.S. had not agreed to halt defensive or counterterrorism operations. Officials said that Gen. Scott Miller, top U.S. commander in Afghanistan, has the authority to order strikes on the Taliban if he deems it necessary.

According to one U.S. official, Wednesday’s strike was a move to convince the Taliban to scale back the attacks against the Afghans that have ramped up over the last 24 to 48 hours. The official said the Taliban had managed to keep attacks at a low level during the seven-day reduction in violence, and the expectation was that the low level would continue.

The official said the Taliban were warned repeatedly about the increased violence, and when the attacks continued to increase in both size and numbers, the U.S. military in Afghanistan determined it was necessary to take action to defend Afghan forces who were under assault.

The U.S. envoy for the peace talks is in Kabul now and Esper said, “he’s going to be pulling the parties back together.”

The White House readout of Trump’s call with Mullah Abdul Ghani Baradar, a co-founder of the Taliban and head of their political office in Qatar, was decidedly more restrained than the president’s own description of the call. Trump told reporters that his relationship with Baradar is “very good” and that the Taliban “want to cease the violence.” By contrast, the readout said that Trump had “emphasized the need to continue the reduction in violence” and urged the Taliban to participate in the intra-Afghan talks.