Lebanon arrested three more nationals suspected of spying for Israel, according to the English-language newspaper Daily Star.
According to the paper, Lebanese security forces detained two men and a woman over the weekend. The Daily Star reported that one of the suspects, Khalil Nabaa, is the brother-in-law of Khulud Nabaa, who was also arrested on charges of spying for Israel.
Lebanon must hand down the death penalty on Lebanese suspects convicted of spying for Israel, Hezbollah leader Hassan Nasrallah said on Friday.
The Lebanese authorities are holding up to 30 suspects in what security sources say is a widening investigation into espionage for Israel. Three of these suspects, who include women, have been arrested in the past 24 hours.
At least 18 suspects have already been charged. Lebanon says at least two spies fled earlier this week to Israel via the border and it demanded that Israel hand them back through UN peacekeepers.
Senior Lebanese security officials have said the arrests have dealt a severe blow to Israel's spy networks in Lebanon.
They say many of the suspects played key roles in identifying Hezbollah targets that were bombed during a 34-day war between Israel and the Shi'ite group in 2006. Some 1,200 people, mostly civilians, were killed in Lebanon. 160 Israelis also died.
Others have been charged with monitoring senior Hezbollah officials and at least one is alleged to have played a role in the 2004 assassination of a commander of the group.
Israel has not commented on the arrests.
"In the name of the families of martyrs, of the wounded and of those who lost their homes... I demand that the death penalty is handed down to the agents who provided information that lead to all these things," Nasrallah, speaking via video-link, told a south Lebanon rally commemorating the ninth anniversary of Israel's withdrawal from Lebanon.
Lebanese courts have handed down what was widely seen as light sentences against Lebanese who have worked with the Israeli occupation and its local militias after Israeli forces ended a 22-year occupation of mainly Shi'ite south Lebanon in May 2000.
Nasrallah said Hezbollah's security services would step up its cooperation with Lebanese security services to root out the spies. He urged any Lebanese dealing with Israel to surrender to the authorities and seek mercy.
