ISMAILIA, Egypt, March 7 (Reuters) - Egypt's coastguard arrested two Palestinians who sailed into Egyptian waters on Sunday and said they were fishing and had strayed into Egyptian waters by mistake, security sources in North Sinai said.

Security incidents, such as shooting in the air when Palestinian boats sail close to the border, have risen in last few months, according to Egyptian security sources. Egypt arrested four Palestinians fishing near the border last month.

The patrol on Sunday arrested Mohammed al-Qiram, 37, and Gamal Noman, 33, as they landed their small fishing boat at the border, the sources said.

Gaza's fishermen are forced by Israeli blockade to fish close to land. Israel controls land, air and sea access to Gaza, under the control of the Islamist party Hamas since 2007.

Egypt, which has a strained relationship with Hamas and a peace treaty with Israel, helps enforce the blockade.

Egypt is building an anchorage for patrol boats on its Gaza sea border to further bolster its defenses against suspected weapons smuggling by Palestinians.

The blockade forces Gaza's 1.5 million inhabitants to rely on goods smuggled through tunnels that provide a supply route for everything from cement to fish.

On Saturday, Egypt intercepted a large quantity of religious and history books ready to be smuggled into Gaza via tunnels.