WASHINGTON, June 30: The US Department of Homeland Security has alerted six major airports in the United States to carefully monitor all travellers of Pakistani origin, including US citizens.

The order was circulated through a DHS memo, warning airports in Washington, New York, New Jersey, Detroit, Chicago and Los Angeles to look for Pakistani travellers with suspected links to terrorists.

The action memo sent to US Customs and Border Protection officials says the suspects may be planning terrorist attacks in the United States between now and the presidential election in November. The memo asks customs officials to look for signs that indicate paramilitary training such as unusual rope-burns, scars and bruises.

The June 17 memo mentions recent Pakistani raids near the Afghan border and Pakistani official sources told Dawn that the initial information about these individuals was collected in the border region between Pakistan and Afghanistan.

The DHS memo indicates that the suspects were "travelling to train at terrorist camps in Pakistan," said an official familiar with the warning.