WASHINGTON — The United States intercepted electronic communications this week among senior operatives of Al Qaeda, in which the terrorists discussed attacks against American interests in the Middle East and North Africa, American officials said Friday.

The intercepts and a subsequent analysis of them by American intelligence agencies prompted the United States to issue an unusual global travel alert to American citizens on Friday, warning of the potential for terrorist attacks by operatives of Al Qaeda and their associates beginning Sunday through the end of August. Intelligence officials said the threat focused on the Qaeda affiliate in Yemen, which has been tied to plots to blow up American-bound cargo and commercial flights.

The bulletin to travelers and expatriates, issued by the State Department, came less than a day after the department announced that it was closing nearly two dozen American diplomatic missions in the Middle East and North Africa, including facilities in Egypt, Iraq, Yemen, Kuwait and Saudi Arabia. Britain said Friday that it would close its embassy in Yemen on Monday and Tuesday because of “increased security concerns.”

It is unusual for the United States to come across discussions among senior Qaeda operatives about operational planning — through informants, intercepted e-mails or eavesdropping on cellphone calls. So when the high-level intercepts were collected and analyzed this week, senior officials at the C.I.A., State Department and White House immediately seized on their significance. Members of Congress have been provided classified briefings on the matter, officials said Friday.