The Hamas Islamist group ruling Gaza has been teaching Egyptian Islamists how to plant bombs in cars, Egyptian state television said on Thursday.
Hamas also gave 400 landmines to Egyptian militant groups, said the television. Hamas is an offshoot of Egypt's Muslim Brotherhood.
Hamas rejected the allegations on Thursday.
"This is completely incorrect," said Fawzi Barhoum, spokesman for the Islamist group. He said that the report was an "attempt to demonize Hamas".
"Security authorities have learned that the military wing of the Hamas movement trained several people to undertake car bombing operations and trained various others to make explosives," said a presenter on state television.
"The military wing of the Hamas movement provided various Salafi jihadists and also other religious currents with 400 landmines. The security apparatus documented this and they will be arrested."
The Brotherhood's Mohamed Morsi was overthrown as Egyptian president by the military in July following mass protests.
Egypt extended a state of emergency
by two months on Thursday because
of the security situation, the presidency said in a statement.
government has accused Brotherhood leaders of inciting the violence and
authorities have imposed a dusk-to-dawn curfew.
Militant attacks against security forces in the lawless Sinai peninsula that borders Israel and the Hamas controlled Gaza Strip have also increased since Morsi was toppled.
Eleven people were killed and seventeen were wounded Wednesday by two explosions
in the northern
Sinai Peninsula in the town of Rafah.
Most of the casualties were
Egyptian soldiers and Ansar Bayt al-Maqdis a group affiliated with
al-Qaida took responsibility for the attacks.