Cairo (CNN) -- Eleven Palestinians have been arrested in the past two days in Egypt's Sinai area, where clashes have erupted in recent days between militants and security forces, a senior Egyptian security official said Saturday.
The detentions in North Sinai come a day after Egyptian security forces arrested nine "terrorists" in the Sinai, according to state-run Nile TV.
Those nine suspects were Egyptian, rather than Palestinian.
The 11 Palestinians had "entered Sinai illegally through the tunnels and could not return due to our operation and shutting down of tunnels," said the senior security official, who is not authorized to speak about the investigation.
One of those arrested is allegedly involved in weapons dealing, he said, adding that the investigation is ongoing.
"We also located the car that was used by attackers who had fired at Al Reissa checkpoint days back. They had abandoned it during a shoot-out with security forces," he said.
A convoy of Egyptian military jeeps mounted with rocket launchers entered the North Sinai port town of El Arish, about 30 miles from the Gaza border, on Saturday afternoon, heading to support the recent military build-up.
Tensions have soared in the wake of a string of violent acts near the Gaza border.
Last Sunday, 16 Egyptian soldiers were killed and seven others were wounded in an attack near the Rafah border crossing, when assailants with semiautomatic weapons and hand grenades stole two armored vehicles from Egyptian forces and tried to enter Israel.
Militants and Egyptian security forces also clashed at a checkpoint at Al Reissa in North Sinai on Wednesday.
Egyptian President Mohamed Morsy on Friday visited the border with Gaza and vowed to bring justice to those affected.
"The blood that was lost, right here in this area, for the sake of our country, was at the hands of treacherous criminals," he said. "We will never, ever rest until we take revenge and bring back justice to those killed."
Morsy said he would restore stability and security to the area.
Morsy visited the military post in Rafah and celebrated the Iftar dinner with troops. He was accompanied by Field Marshal Mohamed Hussein Tantawi, Chief of Staff General Sami Annan and newly appointed Minister of Interior Ahmed Gamal Al Din.
Al Reissa was one of six places that masked gunmen targeted in a coordinated series of attacks in North Sinai that wounded five security officers and a civilian, said Gen. Ahmed Bakr, head of North Sinai security.
Egyptian army Apache helicopters fired rockets Wednesday, causing numerous casualties, Bakr said. Nile TV reported that the strikes killed at least 20 in El Arish.
CNN has not been able to confirm the deaths.
In another attack, masked gunmen on motorbikes fired early Friday at a police station in North Sinai, a police official who is not authorized to speak to the media told CNN. No one was hurt.
That attack came within hours of a meeting between scores of Bedouin leaders and Al Din over stopping the violence.
The interior minister blamed the chaos on the tunnels between Egypt and Gaza, citing them as smuggling routes for terrorists and weapons.
"All tribal chiefs of Sinai agreed to the destruction of all tunnels," tribal leader Mohamed Tarabeeni told CNN. "The minister requested the assistance of the Bedouins in securing the region and protecting the borders the same way they did during the 1967 and 1973 wars with Israel."
The Palestinian Authority spokesman in Gaza, Tahir Al-nono, said Hamas Prime Minister Ismail Haniya, his interior minister and security leaders decided Sunday to close the tunnels from Egypt.
On the Egyptian side of the border, bulldozers and cranes were sent to block the tunnels into Gaza.
The Rafah crossing was opened Friday, but only to allow Palestinians to cross from Egypt to Gaza. It was due to be opened again Saturday.
Hamas, which controls Gaza, condemned Sunday's attack near the crossing as an "ugly crime."
Egypt's military leadership, the Supreme Council of the Armed Forces, has said 35 assailants -- terrorist factions from Gaza -- were involved in Sunday's attack near the Rafah border crossing.
An Egyptian general who works in intelligence in North Sinai told CNN, "There is a high probability that those who committed the Sunday massacre ... are members of Palestinian Islamic Jaljala Army, which is a group considered an offshoot of Hamas but with more radical beliefs."
Sinai has long had its own identity, with many inhabitants -- particularly Bedouins -- not considering themselves Egyptians. They complain of a heavy-handed Egyptian state intruding on their terrain, providing large tracts of land to Cairo-based businessmen and investors, and failing to involve them in developing the region's prosperity.
Journalist Mohamed Fadel Fahmy contributed to this report.