Iran's foreign ministry spokesperson Bahram Ghasemi said the resignation is a plot by the U.S., Israel and the Saudis to foment tensions in Lebanon and the region, the semi-official Iranian Tasnim news agency reported. "Hezbollah is Iran's arm not just in Lebanon but in other Arab countries too", Hariri said.
Mr Hairi said Hezbollah's policies have put Lebanon "in the eye of the storm".
"Over the past decades, Hezbollah has used its weapons against the Lebanese and Syrians to impose a fait accompli in Lebanon", he said, reiterating his rejection of using Lebanon as a platform "to threaten the security of the region".
The coalition government he led brought together nearly all of the main political parties in Lebanon, including Hezbollah.
Hariri's coalition, which took office a year ago, grouped almost all of Lebanon's main parties, including Hezbollah.
"The atmosphere in Lebanon is similar to the situation before the assassination of Rafik Hariri", Hariri said, adding he had feared for some time that he might be assassinated.
Former Lebanese Prime Minister Saad al-Hariri gives a speech during the opening ceremony of the second "Kuwait Financial Forum" in Kuwait City on 31 October 2010.
Several Hezbollah members are being tried in absentia for the killing by a United Nations -backed tribunal in The Hague, Netherlands. The Mediterranean country has a large Christian population as well.
The February 2005 assassination triggered political upheaval that led to Syria's military withdrawal from Lebanon.
He stressed that the "country would be able to overcome political influence exerted by internal and external forces". The group's intervention in Syria is highly controversial in Lebanon.
Iran and Saudi Arabia have a history of tense relations and engagement in proxy conflicts.
"I think the primary driver for this resignation is Saudi Arabia", Slim told CNN.
"Despite my efforts, Iran continues to abuse Lebanon".
The fact that Hariri's announcement was made in Riyadh was an important clue, she said.
"By going after Hezbollah, by denying Hezbollah a credible Sunni partner in governance, it thus weakens Hezbollah on the home front", Slim said. Hariri first took office in June 2009.
The 47-year-old Sunni politician's resignation comes less than a year after his government, to which Hezbollah's political wing belongs, was formed.
Sporting a beard and trademark slicked-back locks, in July Hariri visited the White House and met US President Donald Trump.
"Lebanon is a fragile country".
"Threats to the Lebanese people come from inside as well".
He earlier said that those who cooperate with Hezbollah must be "punished".