Egyptian security forces and Palestinians clashed at the Gaza border on Wednesday over the delay of an international aid convoy, killing one Egyptian border guard and wounding 15 Palestinians. The incident further raises the tension between Egypt and the Hamas rulers of the Gaza Strip who see Cairo's attempts to seal the border as a direct threat to their survival, particularly a new effort to build a steel wall blocking cross-border tunnels. It was the worst violence on the border since an Egyptian major was killed by Palestinian gunmen during Operation Cast Lead in December 2008. The Egyptian state news agency said Palestinians shot and killed the 21-year-old border guard who was in an observation tower overlooking the frontier. Nine other guards were injured by the stones thrown across the border by hundreds of Palestinians. Hamas had called for a protest earlier over the delay of an international aid convoy at the nearby Egyptian port city of El-Arish, but soon lost control of the situation as hundreds of youths began hurling rocks across the border at the guards. Hamas police fired shots to disperse the crowd and shots were also heard from the Egyptian side the border. The director of a local hospital, Dr. Abdullah Shahateh said they treated 12 people, two in a serious condition. There were three other wounded in another hospital. Ehab Ghussein, the spokesman for Gaza's interior minister, said growing anger over Egypt's construction of an underground barrier along its border helped fuel the protests. "There was anger, and that's because of what happened, especially about the wall and (Egypt preventing entry of) the people who are coming to stand with us," he said. Ghussein said 35 Palestinians were injured, including two who are brain dead and five in serious condition. His tally could not be reconciled with that of local doctors. The incident follows a late night clash between international pro-Gaza activists and Egyptian security at El-Arish when Egypt refused to allow part of the convoy to enter its territory and move on to Gaza. More than 50 activists and over a dozen members of the security forces were injured. Activists briefly seized some policemen as well. Egypt has come under criticism from Arab and Muslim groups for cooperating with Israel in its 28-month blockade of the impoverished territory. The blockade was imposed after Hamas violently seized control from the forces of Palestinian Authority President Mahmoud Abbas. The Hamas government has largely survived through a massive network of smuggling tunnels under the border, bringing in everything from food, medicine and consumer goods to cash and weapons. Egypt began constructing an underground metal barrier along its border with Gaza late last year, in its highest profile attempt to control the smuggling. The barrier has angered the Hamas rulers because it would sever Gaza's last lifeline and increases pressure on the militants to make concessions. Egypt says it is no longer affected by Hamas attempts to rally international opinion over the blockade since the border is a matter of national security and sovereignty. "This used to matter before, and we were sensitive to criticism. Now, this is the way it will be," Egyptian Foreign Ministry spokesman Hossam Zaki said about the protests by activists. More than 500 international activists accompanied the convoy organized by the British-based group Viva Palestina, bringing tons of humanitarian supplies, as well as vehicles, to Gaza. The group includes British, American, Jordanian and Turkish activists and lawmakers. The scuffles at the port broke out late Tuesday at al-Arish port building when authorities told the organizers that out of the nearly 200 vehicles, some 59 can't enter Gaza through Egypt, but must go through Israeli terminals. A security official said the vehicles in question are carrying pickup trucks, sedans, generators and other equipment, which are not allowed to pass through the Egyptian crossing at Rafah and had to go via Israel. Only medical aid and passengers are allowed through, the official said. British MP George Galloway told Sky News television that the activists were negotiating with authorities and refusing to leave behind their vehicles. "It's a breach of the agreement which we reached," he said. "It is completely unconscionable." Zaki, the ministry spokesman, said the rules were clear from the start, and accused the activists of coordinating with Hamas to create problems. "We didn't mislead anyone. They have their interests ... and they want to make up problems and clash with Egypt," he told The Associated Press. Television reports showed images of both riot police and activists hurling stones at each other and said clashes began when angry protesters attempted to leave the port area and were driven back by riot police. Alice Howard, a spokeswoman for the group speaking from London, said more than 50 activists were injured in the scuffle. Wael al-Sakka, a Jordanian activist, said the group was not allowed to leave the port building, and denied government claims they took control of the premises. "The Egyptians were too high-strung. The police are the reason for the tension," al-Sakka said. He said six activists were detained, including Americans and British citizens. The security official said five were detained, but didn't identify them. US embassy officials did not immediately have information on the arrests.