DARTMOUTH, Massachusetts (AP) — Federal, state and local authorities are searching the woods near the University of Massachusetts-Dartmouth campus as part of their investigation of the Boston Marathon bombing.

Christina DiIorio-Sterling, a spokeswoman for US Attorney Carmen Ortiz, says the US Bureau of Alcohol, Tobacco, Firearms and Explosives is taking the lead on the search. She could not say what they are looking for but says residents should know there is no threat to public safety.

Suspect Dzhokhar Tsarnaev, who is recovering in a prison hospital after being wounded in a shootout with police, was a student at UMass-Dartmouth.

Three of his classmates are accused of removing a laptop and backpack from his dormitory room before the FBI searched it.

ATF spokeswoman Debora Seifert says no search warrants have been executed and they are searching public areas.

Meanwhile, the Homeland Security Department ordered its border agentsto verify that every international student who arrives in the US has a valid student visa, “effective immediately”, according to an internal memorandum obtained Friday by The Associated Press. The new procedure is the government’s first security change directly related to the Boston bombings.

The order from a senior official at US Customs and Border Protection, David J. Murphy, was circulated Thursday, and came one day after the Obama administration acknowledged that a student from Kazakhstan accused of hiding evidence for one of the Boston bombing suspects was allowed to return to the US in January without a valid student visa.

The student visa for Azamat Tazhayakov had been terminated when he arrived in New York on Jan. 20. But the border agent at the airport did not have access to the information about it in the Homeland Security Department’s Student and Exchange Visitor Information System.

A spokesman for the department, Peter Boogaard, said earlier this week that the government was working to fix the problem, which allowed Tazhayakov to be admitted into the country when he returned to the US.

Tazhayakov and a second Kazakh student were arrested this week on federal charges of obstruction of justice. They were accused of helping to get rid of a backpack containing fireworks owned by bombing suspect Dzhokhar Tsarnaev. A third student was also arrested and accused of lying to authorities.

Copyright 2013 The Associated Press