Story highlights Helicopters heard above Pakistan's capital, Islamabad

Officials intercepted intelligence pointing to a likely attack on a high-value target

Air force and navy commandos are guarding key military installations

Pakistan's capital city of Islamabad is on red alert after officials received information in the form of an intelligence intercept of a likely attack on a high-value target, two senior Pakistani officials told CNN on Sunday.

Helicopters could be heard in the skies above Islamabad as Air Force and Navy commandos searched for suspected militants in the Margalla Hills that surround the city, the officials said.

Key military installations were under tight security.

Among the buildings being guarded are the headquarters for Pakistan's air force and navy, the officials said.

Photos: Embassy closings Photos: Embassy closings Intercepted message spurs embassy closings – A recently intercepted message among senior al Qaeda operatives alarmed the U.S. State Department and led to the closing of 22 embassies and consulates Sunday, August 4, across the Middle East and North Africa. On Sunday afternoon, the State Department said it had extended the closures in 15 of the locations until Saturday, August 10, and added four other posts to the list. Click through to see which facilities are affected, beginning with the U.S. Embassy in Amman, Jordan, which is closed for the week. Hide Caption 1 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. embassy in Dhaka, Bangladesh, was closed August 4 but was scheduled to reopen on Monday, August 5. Hide Caption 2 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in the Saudi capital of Riyadh will be closed for the week along with the consulates in Dhahran and Jeddah. Hide Caption 3 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Muscat, Oman, will remain closed through August 10. Hide Caption 4 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Tripoli, Libya, is closed for the week. Hide Caption 5 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Kabul, Afghanistan, was closed on Sunday and reopened Monday. The consulate in the Afghan city of Mazar-e Sharif was also closed and reopened. Hide Caption 6 of 20 Photos: Embassy closings Intercepted message triggers embassy closings – The U.S. Embassy in Baghdad, Iraq, shown here under construction in October 2007, reopened August 5. The consulates in Basrah and Erbil, which were closed, also resumed normal business on Monday. Hide Caption 7 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Cairo, Egypt, shown here during a demonstration on September 11, 2012, will remain closed. Hide Caption 8 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Antananarivo, Madagascar, was one of four embassies added to the list of facilities to remain closed for the week. The others were the embassies in Burundi, Rwanda and Mauritius. Hide Caption 9 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Sanaa, Yemen, is closed until August 10. Hide Caption 10 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Doha, Qatar, is closed for the week. Hide Caption 11 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Algiers, Algeria, closed on August 4 and reopened the next day. Hide Caption 12 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – Officials announced that they would add the U.S. Embassy in Port Louis on the island of Mauritius to the list of facilities that will be closed for the week. Hide Caption 13 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S Embassy in Kigali, Rwanda, will remain closed for the week. Hide Caption 14 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Khartoum, Sudan, will remain closed for the week. Hide Caption 15 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Manama, Bahrain, will remain closed for the week. Hide Caption 16 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Nouakchott, Mauritania, reopened August 5. Hide Caption 17 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Kuwait City, Kuwait, will remain closed for the week. Hide Caption 18 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Djibouti will remain closed. Hide Caption 19 of 20 Photos: Embassy closings Intercepted message spurs embassy closings – The U.S. Embassy in Abu Dhabi, United Arab Emirates, will remain closed along with the consulate in Dubai. Hide Caption 20 of 20

The officials, from the security and intelligence establishments, did not want to be named given the sensitivity of the information.