Police are continuing efforts to locate someone who made a notably large purchase of ammonium nitrate fertilizer in the Niagara region late last month -- material that could be used in a truck bomb.

RCMP have been asked to assist in the investigation because of the "volatile nature" of such a large quantity of fertilizer, estimated at 65 bags, Sgt. Marc Laporte of the Ontario RCMP told CTV NewsChannel.

Each bag contains 25 kilograms of the potentially explosive fertilizer.

"We take all these threats seriously and we don't have a choice in this kind of matter," he said.

However, more details on the state of the investigation won't be available until at least Wednesday.

Someone walked into Vineland Growers in Lincoln and bought the fertilizer on May 26, which was loaded onto a single-axle trailer and taken away.

"At the time, the male gave staff the impression he was a regular customer; however, upon further review, this was determined not to be the case," Niagara police said in a news release issued Friday.

Investigators are looking into the possibility the man may be a local farmer.

They describe him as being between 40 and 50 years of age, possibly of European descent, who walked with a slight limp and was missing fingers on his right hand.

This comes about as security starts to tighten for the G20 Summit of world leaders in Toronto on June 26 and 27, and the G8 Summit in Huntsville that begins on June 25.

Several law enforcement agencies with involved in providing security for the summit told CTV News that the Niagara Regional Police Service is the lead agency and said any comment should come from them.

A spokesperson for Public Safety Minister Vic Toews said he has been briefed.

Ammonium nitrate, when mixed with diesel fuel, can make a powerful bomb. Such an explosive was used in the 1995 Oklahoma City bombing that killed 168 people.

According to some reports, the quantity of fertilizer involved in the Niagara case is comparable to the quantity used in Oklahoma City.

Ammonium nitrate also played a role in the 'Toronto 18' terror trials. Some of the suspects were arrested following an RCMP sting.

No one in authority has said so far that such a security threat exists to the two summits.

In the period before the Vancouver 2010 Winter Olympics, two tonnes of the fertilizer went missing, which triggered an RCMP investigation.

However, the whole thing turned out to be a clerical error.