South Sinai Governor Khaled Fouda denied that gunmen who killed seven people in attacks on buses in neighbouring Israel on Thursday had fired from Egypt.
At the same time, Egyptian security sources ruled out Israeli claims that Palestinian attackers infiltrated from their territory.
Seven people were killed and 25 wounded when gunmen raked a bus and blasted two other vehicles in southern Israel near the border with Egypt.
Shortly afterwards, Israeli Defence Minister Ehud Barak blamed the Islamist Hamas-controlled Gaza for the attack and criticised Egypt for losing control over security in Sinai and along the border with Israel.
Fouda told reporters that "there was no gunfire from the Egyptian side."
Egyptian security sources, speaking on condition of anonymity, ruled out that Palestinian militants from Gaza to the north slipped past their patrols into Israel.
Israeli security sources said initially that the gunfire appeared to come from the Egyptian side of the border, which runs parallel to Route 12 for several dozen kilometres (miles).
But military spokeswoman Avital Leibovitch told AFP that "everything took place in Israeli territory."
Egypt's military, in charge since a revolt ousted president Hosni Mubarak in February, is carrying out an operation in Sinai to capture Islamist militants who attacked a police station and a gas pipeline to Israel.
Five dead in coordinated attacks in Israel
Gunmen raked a bus with gunfire and blasted two other vehicles on Thursday in a spate of attacks in southern Israel that killed five people and hurt 25, Israeli medics and the army said.
Israel's Defence Minister Ehud Barak quickly laid blame for the attacks on the Hamas-controlled Gaza Strip and pledged that the Jewish state would respond "with all our strength and determination."
The military said the first attack involved gunmen who opened fire on a bus travelling near the border, after which a bomb exploded under a military vehicle which rushed to the scene.
An emergency services spokesman told AFP five people were killed in a third attack on a car travelling on route 90, a road which runs along the Jordanian border and ends at Eilat.
"Five Israelis were killed. Four of them were in a car while the fifth was killed nearby," the spokesman said.
Security sources said the car was hit by a rocket-propelled grenade (RPG) near Beer Ora, some 15 kilometres (nine miles) north of Eilat.
An Israeli military spokeswoman said a "combined terrorist attack" was currently under way "near the Israel-Egypt border, approximately 20 kilometres north of the city of Eilat.
She said at least nine people were injured in the first incident involving a bus.
Shortly afterwards, "several people were injured as a result of an explosive device, detonated at an Israel Defence Force that arrived at the scene and drove over it."
There were also unconfirmed reports on Israel's main television stations that an anti-tank missile had been fired across the border from Egypt.
"There is still an ongoing exchange of fire between our forces and a terrorist squad," she said, describing the two incidents as "a combined attack in a very specific area approximately 20 km north of Eilat."
Security sources had told AFP that the first attack saw an unknown number of gunmen in a car open fire on a bus travelling to Eilat.
They said initially that the gunfire appeared to come from the Egyptian side of the border, which runs parallel to route 12 for several dozen kilometres.
But Leibovitch told AFP that "everything took place in Israeli territory."
There was no immediate information about the identity of the attackers, although there was some initial speculation they may have infiltrated from Egypt.
Shortly after news of the attacks, Israeli Defence Minister Ehud Barak issued a statement blaming Gaza for the attack and criticising Egypt for losing control over security in Sinai and along the border with Israel.
"The source of the terror incidents is Gaza and we will act against them with all our strength and determination," he said in a statement, referring to militants in the Hamas-run territory.
He said the incident reflected the weakness of Egypt's hold on the Sinai peninsula, where Egyptian troops began a massive operation to clamp down on militants this weekend.
"This is a very serious terror incident at a number of locations. The incident reflects the weakness of the Egyptian hold on Sinai and the expansion of activity there by terror elements," he said.
Israel's Channel 2 television showed footage of the bus attacked in the shooting incident standing on a desert road with bullet holes in the windscreen, and several windows shot out.
Several ambulances and tens of soldiers could be seen milling around as two military helicopters were dispatched to help the search for the attackers.