Aoun, a retired army general, was speaking as Kofi Annan, the UN secretary-general, arrived in Beirut on Monday to discuss the ceasefire between Israel and Hezbollah, Aoun's political ally.
"We hope ... a very peaceful change takes place, preserving stability in the country,"Aoun told a news conference.
"If this change does not happen in such a way, there are other ways to escalate from now on."
Aoun, who hopes that Hezbollah will back him in Lebanon's presidential elections next year, supported the Shia group's attacks on Israel and agreed with its reservations over the UN Security Council resolution that ended the fighting.
Lebanon is mainly ruled by a coalition of secularist parties, including the Future Party, led by Saad al-Hariri, and the Progressive Socialist Party, led by Walid Jumblatt, patriarch of the Druze sect.
Aoun's Free Patriotic Movement is one of the most vocal opposition movements in parliament, along with Hezbollah and Amal, another Shia party, which are represented in the cabinet despite being often opposed to the government's decisions.
Aoun's remarks came as Annan arrived in Beirut, to discuss the ceasefire between Hezbollah and Israel.
He called on all sides to implement all parts of UN resolution 1701, calling it "a fixed menu".
Kofi Annan tours war-damaged areas of southern Beirut
"It's not a buffet," he said. "It's not an a la carte menu where you choose and pick. We have to implement 1701 in its entirety and I hope that all parties will pay attention and act in that spirit.
"Without the full implementation of resolution 1701, I fear the risk is great for renewal of hostilities."
Seeking to remove potential sources of friction between the two sides, Annan called on Israel to end its partial sea and air blockade of Lebanon and for Hezbollah to free two Israeli soldiers whose capture on July 12 triggered the month-long war.
"We are working for the lifting of the siege, I am discussing it with the Israeli authorities tomorrow, I hope there will be some movements on this in the not-too-distant future," he said.
Annan said that Hezbollah should hand over the two soldiers to the International Committee of the Red Cross or to Lebanese authorities.
Scores of Hezbollah supporters jeered at Annan during his visit to Beirut's war-ravaged southern suburb, accusing the world body of siding with Israel during the war.
"He came after the war, after the destruction. Why is he here now?"
Shouting "Kofi Annan is an agent of the Americans", and pro-Hezbollah slogans, the crowd surrounded the convoy of the UN chief, forcing him to leave the area minutes after arrival.
"He came after the war, after the destruction. Why is he here now?" said Ashraf Koukha, 25, one of the protesters.
A group of protesters held a poster of Condoleeza Rice, the US secretary of state, with blood-stained vampire teeth as they jeered at the UN chief, accusing him of serving the interests of the United States, Israel's chief ally.
"He is biased towards Israel and America," said 22-year-old Abdel-Sater Selim, a psychology student at the state-run Lebanese University. "There is no justice."
Annan: Militias must disarm
Annan also said that the UN resolution called for the "disarmament and disbanding of all militias" in Lebanon, in a reference to Hezbollah.
During his 11-day tour of the region, Annan will also try to win support for Israel's request for UN troops to be deployed to the Syrian border to prevent Hezbollah from importing weapons from Syria and Iran.
Annan met Hezbollah cabinet members on Monday but has not said what was discussed. Afterwards he toured areas of southern Beirut that had been badly damaged by Israeli bombing.
The UN plans to send 13,000 soldiers to join 2,000 UN troops already in Lebanon and help 15,000 Lebanese troops police the border zone.