A statement by the interior ministry on Tuesday said the group received support from two "Muslim extremists" in Gaza.
It named the first only as Abu Suleiman, saying he provided money, and the second as Majid al-Deri, alleging he trained the Sinai militants in the use of explosives and firearms in the Gaza Strip.
It was the first time Egypt made a direct connection between militants on both sides of the Egypt-Gaza border.
Egypt says the attacks on the Red Sea resorts of Taba in October 2004, Sharm el-Sheik in July 2005 and Dahab last month were all carried out by one group, Tawhid wal Jihad (One God and Holy War), which is led by Nasser Khamis el-Mallahi.
The authorities have described the group as Sinai Bedouins with militant Islamic views, though the group has never issued a statement or claimed responsibility for attacks.
In its Tuesday statement, the ministry said el-Mallahi had sent for training in Gaza the three suicide bombers who carried out the April 24 bombings in Dahab that killed 20 people.
Police killed Mallahi this month and six other suspects since the April Dahab bombings, the statement said. Twenty-two were also arrested in a manhunt in the Sinai peninsula.
The ministry said a detained member of the group, Yousseri Muhareb, had confessed he "received congratulations from these Palestinian elements after carrying out the (Dahab) attacks."
The tourist-packed Dahab resort
was bombed in April
"The Palestinian Majid al-Deiri had ... facilitated the entrance of Yousri Mohareb to the Palestinian territories, his training in bomb-making techniques and use of weapons," the statement said.
The statement said the group believes that Egypt's "state institutions are infidels, and the state's leaders are allied with the enemies of Islam" - a reference to the United States and Israel.
It said the militants got the explosives used in all the bombings from landmines left over in the Sinai peninsula from Egypt's wars with Israel.
Egypt was the first of only two Arab countries to sign a peace deal with Israel in 1979.
The ministry also said that a third Palestinian from Gaza, Tamer al-Nasserat, had planned to come to Egypt to take part in attacks. It did not elaborate.
In the past, Egypt has alluded to ties between the bombings and the Palestinian-Israeli conflict.
After the Taba attack of 2004, in which 11 Israeli tourists were among the 34 people killed, the government said the mastermind was Ayad Said Saleh, an Egyptian-born Palestinian who lived in a refugee settlement in north Sinai.
It said Saleh was motivated by the deteriorating situation in the Gaza Strip, from which his family fled in 1967.
Egypt administered the Gaza Strip from 1949 until 1967. Palestinan and Egyptian families occasionally inter-married, creating long-lasting ties even after the territory was seized by Israel in 1967.