An Israeli naval patrol killed at least four Palestinian militants in diving gear off the Gaza coast on Monday, Hamas security officials and the Israeli army said.

"An Israeli naval patrol spotted a boat with four men in diving suits on their way to carry out a terror attack and fired at them," an Israeli army spokesman said, adding that the patrol had confirmed hitting its targets.

The spokesman did not say what the army thought was the intended objective of the divers.

Hamas security sources said four bodies had been found and a fifth man was missing and presumed dead.

The incident occurred eight days after Israeli marines killed nine Turks in violent confrontations on a Turkish cruise ship which was part of a six-vessel convoy that set out to challenge an Israeli-led blockade of the Hamas-ruled Gaza Strip.

A second attempt by pro-Palestinian activists to break the blockade on Gaza was stopped on Saturday by the Israeli navy without incident.

Israeli media said Monday's sea patrol was carried out by naval commandos from the same unit that boarded the Gaza-bound ships last week. The military spokesman declined to comment on this.

In a second incident in the Gaza Strip on Monday, Hamas security and medical officials said an Israeli aircraft fired a missile at a group of militants in an open area near Gaza City, seriously wounding one man.

An Israeli army spokesman confirmed that a missile had targeted a group of militants trying to fire a rocket at Israel.

Palestinian militants in Gaza frequently try to attack Israeli border patrols and sporadically fire rockets and mortar bombs at Israel. The military spokesman said that more than 10 had been launched at Israel in the past three weeks.

Attempts to attack from the sea are rare, however.

In February, Palestinian militant groups in Gaza sent explosive devices, thought to be primitive sea mines, out to sea intending to hit naval vessels. At least three devices washed up on Israeli beaches and were detonated by sappers.