WASHINGTON - Five students who recently vanished from the Washington area have been arrested in Pakistan, authorities confirmed yesterday, raising fears that they are part of a recent wave of U.S.-based Muslims traveling to South Asia and other extremist hot spots to engage in terrorist activities.

Authorities did not release the names of those arrested but said they were male American citizens around the age of 20. One left a video, which is being analyzed by authorities, in Washington that showed American casualties, according to officials. A voice on the video said Muslims needed to stand up and fight to defend fellow Muslims, according to several sources familiar with the case.

In recent months, authorities have arrested or charged nearly a dozen other Americans or U.S.-based foreign nationals in connection with alleged efforts either to go to Pakistan or Somalia for terrorist training or to recruit and finance the efforts of others. Authorities have portrayed it as an alarming trend that has prompted the FBI, the Department of Homeland Security and other agencies to go on heightened alert.

In this case, the families of five young men who suddenly disappeared went to the Council on American-Islamic Relations, a Washington-based Muslim civil rights and advocacy group. The families and CAIR "immediately determined that the FBI had to be brought into the situation," said the organization's spokesman, Ibrahim Hooper. "Obviously, the circumstances were suspicious enough that we felt it was a matter for law enforcement."

The FBI and Justice Department confirmed the arrests in Pakistan of the five missing men but added they could provide only broad outlines of the case because of an ongoing investigation by U.S. and Pakistani officials.

"We are working with Pakistan authorities to determine their identities and the nature of their business there, if indeed these are the students who had gone missing," said Katherine Schweit, a supervisory special agent with the FBI's Washington field office.

The confiscated video was being studied for content and clues about the men's motives for their trip to Pakistan, the FBI said.

A Washington-based Pakistani official said Pakistani police arrested the men Monday in Sargodha in the Punjab region, a known hotbed of militant activity.

Nadeem Kiani, a Pakistani Embassy spokesman, said one of the men is a Pakistani American, another is Yemeni American and at least one of the other three is Egyptian. Other sources said the three were Egyptian American.

Kiani said the men flew into the southern port city of Karachi on Nov. 30, continued on to Lahore Saturday and then went 100 miles to Sargodha sometime before their arrest.

"While the initial investigation is ongoing, there are many questions. Who they are, what are their nationalities, what was the purpose of their visit to Karachi and Sarghoda, and what were their intentions?" Kiani said. For now, he added, the men have not been charged with a crime and can be held for at least a week while being questioned.

Kiani said the men were arrested because they raised suspicions, especially in light of Pakistan's heightened security after numerous recent militant attacks. "If a person is in a certain area where he does not have apparently any business there, he can be arrested and investigated," Kiani said.

The arrests occurred in the home of an uncle of the Pakistani American student, Kiani said. But he said he could not comment on reports by a Pakistani newspaper that the home was owned by a militant affiliated with Jaish-e-Muhammad, a jihadist group the U.S. has designated a terrorist organization.

The Associated Press said one of the men is Ramy Zamzam, a dental student at Howard University. It said Samirah Ali, head of the university's Muslim Student Association, described Zamzam as "very nice."