Saudi Arabia has accused the Lebanese government of declaring war against it because of Hezbollah's "aggression", further escalating an already tense situation threatening to destabilise Lebanon.

The risk of an open-ended political crisis has loomed large over Lebanon's fragile stability since Saudi-allied Saad Hariri quit as prime minister on Saturday, blaming Iran and its Lebanese ally Hezbollah for "sowing strife" in the region.

The unexpected move has also stoked fears of an escalation in the regional divide between Iran and the Gulf states, primarily Saudi Arabia, with Lebanon on the front lines.

Thamer al-Sabhan, the Saudi minister for Gulf affairs, said on Monday that Lebanon's government would "be dealt with as a government declaring war on Saudi Arabia" because of what he described as "acts of aggression" committed by Hezbollah.

In an interview with Al Arabiya, Sabhan said Hezbollah was involved in every "terrorist act" that threatened Saudi Arabia.

"The Lebanese must choose between peace or aligning with Hezbollah," he added, without offering any details about what action Riyadh might take against Beirut.

There was no immediate response from Lebanon.

Al Jazeera's Zeina Khodr, reporting from Lebanon's capital, Beirut, said the "strong language" used by Saudi officials was described by some analysts as "unprecedented".

"People are concerned ... [by] the very tough rhetoric," she said.

'Two camps'

Hariri, a Sunni politician and longtime ally of the Gulf Kingdom, announced his resignation from the Saudi capital, Riyadh.

His decision brought down Lebanon's coalition government, which included members of Hezbollah.

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"Lebanon is divided into two similar [camps]," political analyst Khaldoun El Charif told Al Jazeera.

"One is pro-Iran and the other is pro-Saudi, which means if things get worse it could lead to a confrontation between the two parties like what happened [in the past]," he added.

"That is why we need to find a solution."

But the constitutional process to appoint a new prime minister has been put on hold, with Lebanon's Justice Minister Salim Jreissati saying there will be no action taken until Hariri returns from Saudi Arabia.

"We have been told by the president that we won't take any decision before knowing the circumstances of Hariri's resignation from the prime minister himself," Jreissati told reporters.

Al Jazeera's Khodr said "it will be hard to find" a political figure to replace Hariri.

"According to Lebanon's power-sharing deal, he must be a Sunni Muslim, and if internal stability is to be maintained he must be a consensual figure able to bring the rival parties together," added Khodr.

"Clearly, the political crisis has now worsened and people are worried that it's going to be a prolonged political paralysis in the country."

In a televised speech announcing his decision to step down, Hariri said he believed he faced threats to his life.

He also called out Iran for sowing "disorder and destruction" in Lebanon, and criticised Hezbollah, which has members in government and parliament as well as an armed wing, for building "a state within a state".

"I say to Iran and its allies - you have lost in your efforts to meddle in the affairs of the Arab world," Hariri said, adding that the region "will rise again and the hands that you have wickedly extended into it will be cut off."

In response, Hezbollah leader Hassan Nasrallah on Sunday called Hariri's resignation a "Saudi-imposed decision".

"It was not our wish for Hariri to resign," he said in a televised appearance on the Hezbollah-owned Al Manar TV.

"Even if he was forced to resign, the way in which it was executed does not reflect Hariri's way in dealing with things," Nasrallah added, questioning the text of Hariri's speech broadcast during his visit to Riyadh.

In his interview with Al Arabiya on Monday, Saudi's Sabhan rejected that the Kingdom had forced Hariri to resign.

"Talk about Hariri being pushed to resign is a lie and aims at distracting the Lebanese people," he said.