KABUL, Afghanistan -- Afghanistan on Sunday hanged six men convicted of terrorism, signaling a tougher approach toward the Taliban.

President Ashraf Ghani's office said he "approved executions of six terrorists who perpetrated grave crimes against civilians and security personnel."

The executions were the first approved by Ghani since he took office in 2014 promising to end the war. His efforts to revive peace talks with the Taliban have failed, and the fighting has escalated.

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A suicide attack in Kabul last month killed 64 people. The Taliban claimed the attack, which was one of the deadliest since the U.S.-led invasion in 2001 drove the extremist group from power.

Soon after, Ghani pledged in a speech to parliament to "deal severely with those who shed the blood of our innocent people and soldiers," and "show no mercy when punishing them."

Deputy presidential spokesman Dawa Khan Menapal said the executed men had been involved in high-profile attacks, including the 2011 killing of Burhanuddin Rabbani, a former president and the head of the High Peace Council, and an attack on a Kabul supermarket that left eight people dead that year.

All six men had been charged and tried according to the law, he added.

The executions would "change the behavior of other terrorists," said independent analyst Maulana Farid. "Now they know that if they are caught they will face the same fate."

The Taliban said earlier this year they would not participate in face-to-face dialogue with the Kabul government, effectively scuttling hopes for reviving a peace process begun last year. Afghan and U.S. officials expect a fierce fight throughout the summer, as the Taliban appear to be on the offensive.

The Taliban issued a statement soon after Sunday's executions deploring the treatment of "vulnerable prisoners" and accusing the Kabul government and the United States of torture, inhumane treatment and "killings under suspicious circumstances."