Apparently we don't know the target but we have have a good idea of the time frame for an attack.

And we do have something of a general idea of the area the attack may occur: the Arabian penninsula. If true, that probably means Al-Qaeda of the Arabian Penninsula (AQAP) is behind it.

Fox News:

The Al Qaeda threat that prompted the State Department to issue a worldwide travel alert and close down 21 embassies and consulates for the weekend is serious and 'very specific,' Rep. Peter King, chairman of the Subcommittee on Counterterrorism and Intelligence, said Friday. 

"We're not certain exactly where something might happen but it's very specific as to when and it's also very specific as to the fact that it is going to happen, so we have to be on alert everywhere," the New York Republican told WINS-AM.

The travel alert was the first of its kind since an announcement preceding the tenth anniversary of the 9/11 terrorist attacks. It came as Washington prepared to close its embassies and consulates throughout the Muslim world this Sunday over security concerns.

U.S. officials have not offered many details on the nature of the threat, but apparently are taking it seriously.

A White House official said Friday night President Obama was being updated on "a potential threat occurring in or emanating from the Arabian Peninsula."

"There is a significant threat stream and we're reacting to it," said Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff. He told ABC News in an interview to be aired Sunday that the threat was "more specific" than previous ones and the "intent is to attack Western, not just U.S. interests."

King, a former chairman of the House Homeland Security Committee told WINS-AM that Americans abroad should register with the U.S. consulates in the countries they are visiting. 

"I would let the American embassy know where you are. Basically check in and where you are and how long you plan to stay there and what your itinerary is," King said.

John Bolton, former U.S. ambassador to the U.N., said the alert indicates the U.S. government must have some "pretty good information" about a possible threat.

The US has been involved in a low-intensity conflict in Yemen for about a decade. It is mostly a drone and missile war but we can assume there are also special forces fighting alongside the Yemeni army who has been most cooperative with the US military in seeking out and killing AQAP operatives.

Our embassy in Yemen has proven to be a target for al-Qaeda before. In 2008, our diplomatic facility was attacked with no loss of life among diplomatic personnel, although an American woman waiting in line for a Visa for her husband was killed. At that time, Yemeni security forces proved themselves adequate in beating off a sophisticated and planned attack.

What about this time?

Fresh intelligence led the United States to conclude that operatives of al Qaeda in the Arabian Peninsula were in the final stages of planning an attack against U.S. and Western targets, several U.S. officials told CNN.

The warning led the U.S. State Department to issue a global travel alert Friday, warning al Qaeda may launch attacks in the Middle East, North Africa and beyond in coming weeks. The U.S. government also was preparing to close 22 embassies and consulates in the region Sunday as a precaution.

The chatter among al Qaeda in the Arabian Peninsula operatives had gone on for weeks but increased in the last few days, the officials said.

Taken together with a warning from Yemeni officials, the United States took the extraordinary step of shutting down embassies and issuing travel warnings, said the officials, who spoke on condition of anonymity.

While the specific target is uncertain, U.S. officials are deeply worried about a possible attack against the U.S. Embassy in Yemen occurring through Tuesday, the officials said.

The warnings also come as news has surfaced that al Qaeda's leader, Ayman al-Zawahiri, has appointed the head of al Qaeda in the Arabian Peninsula, Nasser al-Wahishi, as his overall general manager of the terror network, Seth Jones of the Rand Corporation said. 

The alert has almost certainly altered the terrorists' plans if they did indeed, want to attack our embassy in Sanaa. Knowing how thorough al-Qaeda can be, it wouldn't be a stretch to imagine them with a "Plan B" in case the operation was compromised.

The next few days will be tense ones in Yemen.