Egypt began the trial on Sunday of 26 men suspected of links with Lebanon's Hezbollah and who face charges that include planning attacks inside Egypt.
The case has highlighted the worries of conservative Sunni states like Egypt and Saudi Arabia about the increasing influence of Shi'ite Iran and groups, like Hezbollah, seen as Tehran's proxies.
Egypt's announcement in April that it had detained the men heightened tensions with the Lebanese guerrilla group, which had angered Cairo this year by accusing the Egyptian authorities of complicity with Israel in its siege of Gaza.
The charges against group members, read out in the emergency state security court, included giving information to a foreign organization, planning attacks inside Egypt targeting tourist sites and the Suez Canal, and possession of explosive material.
All those present denied charges brought against them. The men are not all facing the same charges.
Rights groups say Egypt has used "exceptional" courts like emergency and military courts to secure guilty verdicts and point to swift and often harsh sentences passed by the courts against Islamist militants in the 1990s.
"We live and die as Egyptians. We will never betray our country," several of the Egyptian defendants said from the cage where they were held in court when the charges were read out.
Others chanted during proceedings "We sacrifice ourselves to you, oh messenger of God," a reference to the Prophet Mohammad.
Lawyer Saad Hasaballah said four men were being tried in absentia and two others were not present in court on Sunday.
The men being tried include two Lebanese, five Palestinian and one Sudanese. The rest are Egyptian.
Among those being tried in absentia is Lebanese citizen Mohamed Qublan, while the second Lebanese, Sami Chehab, also named as Mohamed Youssef Mansour Ahmed, was in court.
Charges against the two Lebanese men included recruiting and financing the group and planning "terrorist" actions.
Hezbollah leader Sayyed Hassan Nasrallah said in April that Chehab was a member of the Lebanese group and was detained in November but said he was helping provide military equipment to support Palestinians in their fight against Israel.
Nasrallah said Chehab was being helped by up to 10 others but said others detained by the Egyptian authorities had no link to Chehab.
Judge Adel Abdel-Salem Gomaa referred one of the accused for medical checks after he said he was tortured.
The court set the next hearing for October 24.