Federal authorities have doubled a reward to $20,000 for information about the theft of 704 pounds of dynamate stolen from a construction site in Pennsylvania last weekend.

The dynamite and 400 blasting caps were reported missing Monday from a gas pipeline worksite in Marietta, Pennsylvania, according to officials with the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The ATF initially announced a $10,000 reward but doubled the amount Thursday morning. The money is offered for the recovery of the stolen explosives and/or the arrest and conviction of those responsible.

The Gregory General Contracting Company on Monday reported the large theft of explosives in Lancaster County.

The explosives were stored inside a locked truck trailer left on the site after workers left on Friday. The worksite security company did not discover the theft until Monday, when they noticed the trailer door was ajar with the locks missing, the ATF said.

"The ATF, along with our law enforcement partners are working very diligently and with a sense of urgency to recover the stolen explosives and to find those responsible for the theft," said Donald Robinson, Special Agent in Charge. "We are asking for the public's help in our effort to locate these explosives and to apprehend and convict those responsible."

"The amount of explosives taken has led us to take this very seriously," said ATF Special Agent Charlene Hennessy.

Hennessy said the ATF has no reason to believe the explosives are in the hands of terrorists but noted the agency "is running down every lead."

"It's too early to speculate on a motive," she said. "But we don't have any reason to believe it's terror-related."

The ATF released photos of the type of dynamite stolen to show the public "what to look for," Hennessy said.

More than 700 pounds of dynamite and 400 blasting caps were stolen from a construction site in Lancaster County, Pennsylvania. (Photo courtesy of the ATF)

The Gregory General Contracting Company is a subcontractor of Williams Partners, which is managing the Atlantic Sunrise pipeline project in Lancaster County.

Among the theories investigators are looking at is that the crime may have been committed by a group or individual protesting construction of the pipeline, which will cut through 37 miles in Lancaster County, Pennsylvania.

Last fall, about 35 protesters participated in an 18-vehicle blockade of an access road being built to accommodate construction work, according to LancasterOnline.com.

Theft and possession of stolen explosives is a federal crime punishable by up to 10 years in prison.

Anyone with information is asked to call the ATF at 1-888-ATF-BOMB (1-888-283-2662). Tips can also be submitted by using the Reportit(r) app, available from Google Play and the Apple App store, or by visiting www.reportit.com.

Example of the type of detonator or blasting cap stolen from worksite in Lancaster County, Pennsylvania. (Photo courtesy of ATF)

Anthony G. Attrino may be reached at tattrino@njadvancemedia.com. Follow him on Twitter @TonyAttrino. Find NJ.com on Facebook.