LAGOS, July 5 - Nigerian militants said on Sunday they had launched their third attack on Royal Dutch Shell since President Umaru Yar’Adua made an amnesty offer, and threatened to intensify their campaign of sabotage.

The Movement for the Emancipation of the Niger Delta (MEND) said in an emailed statement it had attacked a Shell oil well head in the Cawthorne Channel at about 0200 GMT, again dashing hopes that the amnesty offer would buy a period of calm.