WASHINGTON—President Trump said Saturday he called off a planned Camp David summit with Taliban leaders and Afghan President Ashraf Ghani after a Taliban bomb attack in Kabul killed an American soldier.

On Twitter, Mr. Trump said the Afghan government and Taliban officials had been coming to the U.S. Saturday night. The president’s tweets reflected his most extensive direct involvement in the monthslong talks.

“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,” he wrote. Following the attack, “I immediately cancelled the meeting and called off peace negotiations. What kind of people would kill so many in order to seemingly strengthen their bargaining position?”

On Thursday, the Taliban claimed responsibility for a suicide car bombing in the east of the Afghan capital that killed at least 11 people, including a Romanian and an American soldier, and wounded dozens.

Following Thursday’s attack, Mr. Ghani described peace with the Taliban as “meaningless.”

On Friday, the Pentagon identified the killed service member as Army Sgt. 1st Class Elis A. Barreto Ortiz, 34 years old, from Morovis, Puerto Rico. Sgt. Ortiz’s remains are expected to arrive at Dover Air Force Base in Delaware late Saturday night, the Pentagon said.

The Wall Street Journal reported Friday that Mr. Ghani was planning to travel to the U.S. for talks with Mr. Trump, in an apparent bid to shape a peace deal that has so far excluded the Afghan government and been met with criticism in Washington. The Taliban have refused to hold direct talks with any Kabul administration, which it views as illegitimate.

Read more at The Wall Street Journal