President Donald Trump said in an interview broadcast Monday that he wants to withdraw US forces from Afghanistan, but will leave a strong intelligence presence there to counter what he termed the "Harvard of terrorists."

The Taliban, who on Monday killed six people with a powerful bomb targeted at Afghanistan's defense ministry, have refused to negotiate with President Ashraf Ghani, and a previous attempt to bring the insurgents together with government officials in Doha collapsed in April in a dispute over attendees.

Germany, a key player in international support for the post-Taliban government, and Qatar, which maintains contacts with the militants, said that they jointly extended invitations for a dialogue in Doha on Sunday and Monday.

The Afghans "will participate only in their personal capacity and on an equal footing," Markus Potzel, Germany's special representative for Afghanistan and Pakistan, said in a statement released Monday by the United States.

"Afghanistan stands at a critical moment of opportunity for progress towards peace," he said.

"An essential component of any process leading to this objective will be direct engagement between Afghans," he said.

The meeting comes after US Secretary of State Mike Pompeo paid a previously unannounced visit last week to Kabul where he voiced hope for a peace deal with the Taliban "before September 1."

The ambitious timeframe would allow a deal before Afghanistan holds elections in September, which Western officials fear could inject a new dose of instability.

Trump wants to pull all US troops from Afghanistan, believing that America's longest war -- launched after the September 11, 2001 attacks -- no longer makes military or financial sense.

But he said the US will "be leaving very strong intelligence, far more than you would normally think," in an interview with the Fox News Channel's "Tucker Carlson Tonight."

"It just seems to be a lab for terrorists... I call it the Harvard of terrorists," Trump said.

- Taliban attack wounds children -

The Taliban have refused to halt their violence, believing that they have the upper hand as the United States is eager to leave.

Monday's bombing was followed by Taliban gunmen storming a nearby building, trigging a gunbattle with special forces.

The bombing and shootout wounded dozens of people, including 50 children, most of whom were hurt by flying glass, officials said.

Save the Children branded the strike "utterly deplorable," warning that "children's smaller bodies sustain more serious injuries than adults" and that the trauma of such attacks can stay with them for years.

The White House condemned the "brazen" attack, saying it "demonstrates the Taliban's callous disregard for their fellow Afghans, who have repeatedly voiced the urgency of finding a peaceful resolution to the conflict."

But Washington made no move to interrupt its seventh round of talks with the Taliban in Doha that started on Saturday.

"Once the timeline for the withdrawal of foreign forces is set in the presence of international observers, then we will begin the talks to the Afghan sides, but we will not talk to the Kabul administration as a government," tweeted Suhail Shaheen, the spokesman for the Taliban's office in Qatar.

Under a peace deal, the United States plans to pull its roughly 14,000 troops from Afghanistan.

In return, the Taliban would provide assurances that they will never allow their territory to be a base for foreign attacks -- the primary reason for the US invasion nearly 18 years ago.

Zalmay Khalilzad, the US negotiator with the Taliban, said that dialogue among Afghans was an essential part of a peace deal.

"Mutual acceptance, seeking consensus, and agreeing to resolve political differences without force is what is needed to learn from the tragedy of the last 40 years," Khalilzad said, referring to Afghanistan's nearly incessant conflict since the Soviet invasion in 1979.

"I wish participants success," he tweeted.