Donald Trump says he has cancelled secret peace talks on Afghanistan scheduled for Sunday that would have brought him face to face with Taliban leaders at Camp David, the presidential retreat in the hills of Maryland state – with the Islamist militant group warning on Sunday that the snub meant more American lives would be lost.

The US president made the remarkable claim in a series of tweets on Saturday evening declaring he had “called off” the negotiations after the Taliban claimed responsibility for a blast in Kabul that killed 12 people including a US soldier on Thursday.

“What kind of people would kill so many in order to seemingly strengthen their bargaining position?” Trump wrote, accusing Taliban leaders of trying to build leverage ahead of Sunday’s talks.

“If they cannot agree to a ceasefire during these very important peace talks, and would even kill 12 innocent people, then they probably don’t have the power to negotiate a meaningful agreement anyway.”

Unbeknownst to almost everyone, the major Taliban leaders and, separately, the President of Afghanistan, were going to secretly meet with me at Camp David on Sunday. They were coming to the United States tonight. Unfortunately, in order to build false leverage, they admitted to.. — Donald J. Trump (@realDonaldTrump) September 7, 2019

....only made it worse! If they cannot agree to a ceasefire during these very important peace talks, and would even kill 12 innocent people, then they probably don’t have the power to negotiate a meaningful agreement anyway. How many more decades are they willing to fight? — Donald J. Trump (@realDonaldTrump) September 7, 2019

The revelation of the planned talks and their abrupt cancellation leave a question mark over the future of peace talks intended to bring American involvement in Afghanistan to an end, an early and regularly recited Trump campaign pledge.

The Taliban warned on Sunday that the cancellation meant more American lives would be lost, while the United States promised to keep up military pressure on the militants.

Zabihullah Mujahid, a Taliban spokesman, criticized Trump for calling off the dialogue and said US forces have been pounding Afghanistan with attacks at the same time.

“This will lead to more losses to the US,” he said in a statement. “Its credibility will be affected, its anti-peace stance will be exposed to the world, losses to lives and assets will increase.”

The secret plans by Trump emphasised how much faith the US president puts on personal diplomacy, even with people previous heads of state would have avoided meeting for fear of granting them imprimatur – now apparently including members of a militant group the US government officially classifies as terrorists.

The Taliban had confirmed in a statement that it had been asked in late August by Trump to visit the US.

“While America and Afghan allies have killed hundreds of Afghans, it doesn’t show patience and experience to react to an attack [by the Taliban] prior to signing the deal.”

The militant group vowed to continue its jihad but left open the possibility of resuming negotiations. “If the way if talks is chosen instead of war, we are committed to that until the end,” it said.

Suhail Shaheen, a spokesman for the Taliban’s political office in Doha, where negotiations have been taking place, said an agreement had been “finalised” a few days ago and that both sides agreed the deal would be announced by the Qatari government.

“Everyone was satisfied,” he wrote on Twitter. “At this time, the disappointing President Trump’s tweets have been unbelievable and certainly damaged his credibility.”

The Illinois congressman Adam Kinzinger, a fellow Republican, wrote on Twitter: “Never should leaders of a terrorist organisation that hasn’t renounced 9/11 and continues in evil be allowed in our great country. NEVER. Full stop.”

American negotiators said they had reached an “agreement in principle” with Taliban leaders over nine rounds of talks in Qatar aimed at facilitating the withdrawal of the roughly 13,000 US troops who remain in Afghanistan nearly 18 years since the military campaign commenced.

The Camp David talks would have been held three days short of the anniversary of the 11 September 2001 terrorist attacks by al-Qaida militants who were being harboured in Afghanistan by the then ruling Taliban regime, the justification for the US-led invasion of the country a few weeks later.

Most of the terms of the provisional peace agreement are classified but it would include the withdrawal of 5,000 American soldiers from five bases across Afghanistan by early next year. The Taliban would agree to renounce al-Qaida, fight the Islamic State group and stop jihadists from using the south Asian country as a safe haven.

The US secretary of state Mike Pompeo said on Sunday that talks could be reopened with a “a significant commitment” from the Taliban.

﻿Bloodletting has continued in the battered country despite the negotiations, including a car bomb blast on Thursday a fortified area near the green zone.

The death of the American soldier was at least the 16th of a US serviceperson in Afghanistan this year. A Taliban spokesman claimed responsibility for the attack on Twitter.

More than 1,200 civilians have been killed so far this year in the country, most as a result of airstrikes by US warplanes including 89 children, according to figures by the UN Assistance Mission in Afghanistan that the US government disputes.

The withdrawal agreement has been criticised by Afghanistan’s internationally recognised president, Ashraf Ghani, whose government was excluded from the talks as a condition of the Taliban sitting down at the table.

“The government considers the Taliban’s obstinacy to increase violence against Afghans as the main obstacle to the ongoing peace negotiations,” said a spokesman for Ghani on Sunday.

Activists have also said a US withdrawal would have dire implications for ordinary Afghans, especially women, who might be subject to extreme religious restrictions in a future Taliban-run or dominated national government.

• Akhtar Mohammad Makoii contributed to this report from Herat and Reuters also contributed