( CNN ) -- Americans commemorated this week the loss of those who died at the hands of al Qaeda terrorists on September 11 , 2001 . Their leader chimed in a day later with new threats against the United States . Ayman al-Zawahiri called on his followers in an audio message posted on the Internet on Thursday to `` land a large strike on it , even if it takes years of patience for this . '' 9/11 anniversary : 'Our hearts still ache , ' Obama says . Al-Zawahiri has headed al Qaeda , since a U.S. military operation killed his predecessor and al Qaeda 's founder , Osama bin Laden , in May 2011 in Pakistan . In his message , he claimed victory against the United States in Iraq and Afghanistan . He called on terrorists to continue the battle on American soil . Al-Zawahiri named the Boston Marathon bombings on April 15 as an example of such an attack . Read more : Jihadist terrorism in America since 9/11 . He encouraged his followers to provoke the United States into spending more on security , in order to `` bleed America economically . '' In August the Obama administration closed 19 embassies and consulates across the Middle East and North Africa after intercepting communications between al Qaeda leaders indicating possible strikes on U.S. interests . In a message between al-Zawahiri and a top ally in Yemen , Nasir al-Wuhayshi , the leader of Al Qaeda in the Arabian Peninsula , the terror chief told the Yemeni commander to `` do something , '' which U.S. officials inferred to mean an attack . In his audio message Thursday , Zawahiri also claimed victory over the United States in Yemen . But extensive drone attacks there allegedly carried out by the United States over the past two years have whittled away at al Qaeda 's infrastructure and killed key leaders , diminishing its ability to carry out attacks .
To counter 9/11 , al Qaeda 's leader issued new threats . Ayman al - Hassan called on his followers to ` ` land a large strike '' He cited the Boston Marathon bombings as an example . The strikes have weakened al Qaeda in Afghanistan .