PARIS, May 4 — French police are scrambling to locate 1,100 pounds of fertilizer that could be used to make a powerful bomb after the material was discovered missing on Monday in northern France.

The fertilizer, ammonium nitrate, is believed to have been stolen over the Easter weekend from the port of Honfleur near the mouth of the Seine river, according to officials quoted by local media. The officials said large quantities of the fertilizer were stored at the port without any particular security measures.

Ammonium nitrate is highly explosive when mixed with diesel or fuel oil and has been used for some of the most destructive terrorist bombs in recent history, including the 1995 Oklahoma City bombing and the bombings that killed 62 in Istanbul last year.

[. . . .] While the Madrid bombs were not made with ammonium nitrate, two unexploded bombs found on French rail lines in recent months did contain the fertilizer. [. . . .]

In late March, British police seized more than half a ton of the fertilizer in West London in a raid on suspected Islamic terrorists. [. . . .]