MADRID — Spain’s navy rammed a Greenpeace dinghy during a protest in the Atlantic Ocean against oil exploration near the Canary Islands on Saturday, injuring four of its activists, one of them seriously, the environmental organization said.

However, the navy disputed that account. The navy said it dispatched two boats from one of its ships in the area to prevent Greenpeace from boarding a large oil drilling ship and that one of its activists was seriously injured when she fell out of her dinghy and was hit by its propellers.

Speaking by radio-telephone from Greenpeace ship Arctic Sunrise in the area, Capt. Joel Stewart identified the woman as a 23-year-old Italian activist and said the three other injuries were minor.

The navy said it rushed the activist to a Spanish hospital in a helicopter.

Some residents fear that oil spills could damage the Canary Islands, which are one of Europe’s major tourism magnets and home to an important fishing industry.