* Eygpt state security accuses Hezbollah of plotting attacks
* Public prosecutor investigates
* Probe may heighten tension with Iran
(Refiles adding dropped words in last paragraph; adds details, background, analyst comment)
By Will Rasmussen
CAIRO, April 8 (Reuters) - Egyptian authorities accused the Lebanese group Hezbollah on Wednesday of planning attacks inside Egypt, a development that could plunge Cairo's relations with the Shi'ite group's backer, Iran, to new lows.
The office of Egypt's public prosecutor said it was investigating accusations that Hezbollah had recruited a 49-member cell with the aim of striking inside Egypt, a key U.S. ally in the Middle East.
Hezbollah angered Egypt earlier this year by accusing Cairo of complicity with Israel in its siege of the Gaza Strip.
"The public prosecutor received a note from state security about information confirmed by questioning about Hezbollah leaders sending some elements to the country to attract members to work with the organisation ... with the aim of carrying out acts of aggression inside the country," a statement by the public prosecutor said.
The statement said the group had been trying to monitor Egypt's Suez Canal, its border with the Gaza Strip, and tourist installations in the Sinai Peninsula and sending information back to Hezbollah.
It also said the group had been establishing links with criminal elements to forge passports and setting up businesses to cover for spying activities.
It gave no details of any attacks being planned, but accused Hezbollah of trying to spread Shi'ite ideology in Egypt.
HAMAS AND HEZBOLLAH
A lawyer for Hezbollah said on Tuesday that about 50 men, including Egyptians, Palestinians and Lebanese, had been brought in for questioning on Saturday on suspicion of helping Hezbollah and the Palestinian militant group Hamas, which runs the Gaza Strip.
The Egyptian government is worried that public support for Hamas may boost the popularity of the Muslim Brotherhood, which has ideological and historical ties with the Palestinian group and is the strongest opposition group in Egypt.
Both Hamas and Hezbollah are supported by Iran, whose growing influence in the region has alarmed conservative Arab states, including many in the oil-exporting Gulf region.
Hezbollah leader Hassan Nasrallah called in December for the Egyptian people and armed forces to compel their leaders to open Egypt's border with Gaza to lift the Israeli-imposed siege on the coastal strip.
Egypt said Nasrallah's call was an appeal for mutiny and accused Nasrallah of insulting the Egyptian people.
"This will add some fuel to the Egyptian-Iranian political confrontation," said Abdel-Monem Said, director of the Cairo-based Al-Ahram Centre for Political and Strategic Studies.
"If there is firm evidence, the people in the Gulf could take it seriously. If they (Hezbollah) try to branch into Egypt, that means the possibility in the much closer Gulf countries could be high."
Said said it would be feasible for Hezbollah to set up cells in Egypt, but members of the group could also be personal admirers of Nasrallah, whose opposition to Israel has made him a popular hero in the Arab world, rather than his agents.
Egypt is eager to show it is doing all it can to stop money or aid reaching Hamas, which is at odds with Fatah, the rival movement that holds sway in the West Bank.
Mainly Sunni Muslim Egypt and Shi'ite Iran have not had full diplomatic relations since Iran's 1979 Islamic Revolution, when Iran cut ties after former president Anwar Sadat hosted the deposed shah in Cairo. (Writing by Will Rasmussen; editing by Tim Pearce)