The United States has said its landmark deal with the Taliban has entered the “next phase” while urging the militants to reduce rising violence to allow Afghan peace talks to begin.

The two sides signed an agreement in February that saw Washington pledge to withdraw all troops from Afghanistan by the middle of next year, in return for the insurgents promising to hold negotiations with the Afghan government to end the decades-old war.

Under phase one, the US said it would reduce troops to 8,600 within 135 days, while completely removing forces from five military bases.

On the 135th day, US Special Representative on Afghanistan, Zalmay Khalilzad, who negotiated the deal for Washington, tweeted that both sides had reached a “key milestone”.

“The US has worked hard to carry out 1st phase of its commitments under the agreement, including to reduce troops & depart five bases,” he said on Monday.

As the deal entered its “next phase”, Washington's approach will be based on certain conditions, Khalilzad warned. “We will press for completion of prisoner releases, reduction of violence [...] & start of & progress in intra-Afghan negotiations,” he said.

Talks between the Taliban and Kabul hinge on a nearly completed prisoner exchange agreed in the deal.

Kabul pledged to free some 5,000 Taliban prisoners in a swap that would see the insurgents release around 1,000 Afghan security force captives. The government has so far released more than 4,000 Taliban inmates, while the insurgents have freed more than 600 Afghan security personnel.

Since the deal was signed, the Taliban have stepped up attacks across much of Afghanistan killing hundreds.

Read: Brutal Afghan attacks highlight limitations of US-Taliban deal

Khalilzad too condemned the violence, saying “large numbers” of Afghans continued to die without a reason, while acknowledging that no American had been killed since the deal.

“Violence has been high, especially in recent days and weeks,” Khalilzad said, condemning a Taliban attack on Monday on a rural office of Afghanistan's intelligence agency that killed 11 security personnel.

“The Taliban's attack [...] contradicts their commitment to reduce violence until a permanent ceasefire is reached in intra-Afghan talks.“