A worldwide travel alert has been issued by the State Department due to a threat of terrorist attacks from al-Qaida and it’s affiliated organizations. The alert was issued Friday and is said to last until August 31.

“Current information suggests that al-Qaida and affiliated organizations continue to plan terrorist attacks both in the region and beyond, and that they may focus efforts to conduct attacks in the period between now and the end of August,” the department said in a statement.

The primary focus is on al-Qaeda in the Arabian Peninsula, a terrorist group that is based in Yemen and a small part of Saudi Arabia, according to Representative Peter King and the two United States officials. King said that this threat is “the most specific I’ve seen” since the attacks on the United States on Sept. 11, 2001. “It is coming out of Yemen, and it is al-Qaeda in the Arabian Peninsula,” King said on CNN. “There is a plot, the attacks are planned, but it’s not certain as to where. Al Qaeda is in many ways stronger than it was before 9/11, because it’s mutated and it spread and it can come at us from different directions, and al Qaeda in the Arabian Peninsula is probably the most deadly of all the al Qaeda affiliates,” he said.

“This is the most serious threat that I’ve seen in the last several years,” Senator Saxby Chambliss of Georgia, said on NBC’s “Meet the Press” program. “There’s been an awful lot of chatter out there” among terrorists planning attacks, Chambliss said, noting that this was “reminiscent of what we saw pre-9/11.”

The State Department said that it would close at least 18 diplomatic posts in the Middle East and surrounding areas because of the threats on Thursday. On Friday, it confirmed that it would be closing 21 posts within the region.

The full release from the State Department is below:

The Department of State alerts U.S. citizens to the continued potential for terrorist attacks, particularly in the Middle East and North Africa, and possibly occurring in or emanating from the Arabian Peninsula. Current information suggests that al-Qa’ida and affiliated organizations continue to plan terrorist attacks both in the region and beyond, and that they may focus efforts to conduct attacks in the period between now and the end of August. This Travel Alert expires on August 31, 2013.

Terrorists may elect to use a variety of means and weapons and target both official and private interests. U.S. citizens are reminded of the potential for terrorists to attack public transportation systems and other tourist infrastructure. Terrorists have targeted and attacked subway and rail systems, as well as aviation and maritime services. U.S. citizens should take every precaution to be aware of their surroundings and to adopt appropriate safety measures to protect themselves when traveling.

We continue to work closely with other nations on the threat from international terrorism, including from al-Qa’ida. Information is routinely shared between the U.S. and our key partners in order to disrupt terrorist plotting, identify and take action against potential operatives, and strengthen our defenses against potential threats.

We recommend U.S. citizens register their travel plans with the Consular Section of the U.S. Embassy through the State Department’s travel registration website. We strongly recommend that U.S. citizens Traveling abroad enroll in the Department of State’s Smart Traveler Enrollment Program (STEP). STEP enrollment gives you the latest security updates, and makes it easier for the U.S. embassy or nearest U.S. consulate to contact you in an emergency. If you don’t have Internet access, enroll directly with the nearest U.S. embassy or consulate.