Egyptian border and security authorities have arrested 3 Palestinians and Egyptians in the Sinai region, including one who was wearing an explosives belt and had crossed from Gaza to Egypt in an underground tunnel, security officials said Wednesday. The authorities put their security forces in northern Sinai on high alert Wednesday in a bid to make sure that no more armed people were at large. Police set up more checkpoints and border guards were seen using iron poles to probe the ground near the newly found tunnel in a search for more. One of the Palestinian detainees, a man in his early 20's, was caught Tuesday as he tried to cross the Gaza-Egypt border in an underground tunnel near the Egyptian border city of Rafah. He had wrapped himself in an explosives belt, said the soldier who caught him, Mohammed Abdel Wahab. The arrested man told Egyptian state security officials that he had been plotting an attack with other Palestinians in Sinai, said an official. Eyewitnesses said heavy Egyptian security forces on Wednesday morning surrounded a building in Rafah and arrested two other Palestinians. The security official said the two arrests were linked to the alleged suicide attack plot. The building's owner, Mohammed Salem, said one of the Palestinian men had rented an apartment in the building a week ago and had been joined Wednesday by the other. Egypt has suffered a string of suicide terror attacks in recent years at Sinai tourist resorts. Egypt, Israel and the Palestinians have also debated how best to control the border with Gaza, to prevent smuggling of weapons into Gaza and the infiltration of extremists into Egypt.