Detainees are said to be of Pakistani, Yemeni and Egyptian origin, but US and Pakistani officials refuse to discuss their identities.
Police in Pakistan say five American nationals they arrested this week in an eastern town have told interrogators they arrived in the country to join "jihad" or a holy war.
U.S and Pakistani officials are interrogating the detainees who are said to be in their 20s and come from northern Virginia. Local police say they the men were arrested at a house in the city of Sargodah and that all of them have admitted they had come to Pakistan for "jihad" or holy war.
Speaking by telephone, district police chief Usman Anwar told VOA his men watched activities of the suspects for nearly two days before arresting them.
"We had suspicion that they were carrying out some nefarious activities while being in Sargodah," said Anwar. "We watched them and we have interrogated them, we have looked at their computers and the electronic data and the maps that they had and the E-mails have been checked, the mobile details have been received and everything points out to that they were about to commit some serious crime."
A U.S Embassy spokesman says Pakistani and American officials are closely coordinating in gathering more information on the suspects. But he would not comment on reports in local media that an FBI team is in the country in connection with the investigation.
The detainees are said to be of Pakistani, Yemeni and Egyptian origin. But U.S and Pakistani officials have refused to discuss their identities.
"I would not get into specifics, but what I understand is that people who have been arrested are U.S nationals, but some of them of Pakistan origin, some of them of other descent. So let us not get into specifics at this stage," Abdul Basit, the spokesman for Pakistan's Foreign Ministry.
The five American suspects were said to be in contact with an outlawed Pakistani militant group, Jaish-e-Mohammad (Army of the Prophet Mohammad), that has links with al-Qaida and Taliban extremists.
Pakistan is an ally in the U.S.-led war against terrorism and has been under pressure from Washington to intensify efforts to root out extremists blamed for launching attacks on coalition forces across the border in Afghanistan.