The United States has commemorated the 18th anniversary of the September 11 attacks in Washington and New York, while President Donald Trump has vowed to strike the Afghan Taliban in a "stronger form" than ever.
President Trump attended a memorial service in Washington, while another ceremony was held in New York with speeches by the families of the victims.
The attacks in 2001 left more than 3,000 people dead and adopted by al Qaeda. Following the attacks, the United States launched an international war against terrorism in which Iraq and Afghanistan were occupied.
Trump vows
In a speech marking the anniversary of the attacks, US President Donald Trump said his country was not seeking conflict, but would respond with full force to any aggression against it.
Trump added that if anyone dares to attack our land, we will respond with all the strength and iron will of the American spirit, and this spirit is unbreakable.
He pointed out that peace talks were scheduled a few days ago - intended with the Taliban - but "canceled them when I learned that they had killed a great American soldier from Puerto Rico and 11 innocent people, they thought they would use this attack to show strength but in reality what they showed is infinite weakness for him".
Trump said US forces "have hit our enemy more aggressively in the past four days than they have been, and will continue to do so."
"If they go back to our country for any reason, we will chase them where they are, and we will use a force that Washington has never used before.
Trump's threats come at a time when al Qaeda, which launched the September 11 attacks, released a video calling for attacks against US, European, Israeli and Russian interests.
In the 33-minute recording, the group's leader Ayman al-Zawahri criticized what he called "laggards" about jihad, according to the US-based SITE Center, which monitors jihadist sites.
Trump announced on Saturday that he was about to meet with leaders of the Taliban movement, which was harboring al Qaeda in Afghanistan, at the Camp David presidential resort on Sunday.