Hassan Nasrallah, the head of Lebanon-based Hezbollah group, and Mahmoud Ahmedinejad, the Iranian president, have issued stern warnings to Israel, saying that any aggression on that country's part would be met with a swift armed response.
Nasrallah, speaking during a televised address from Beirut on Friday, said that his fighters will make the lives of Israelis "a living hell" if it is attacked.
"There are targets in occupied Palestine [Israel] which could be targeted by a small number of missiles," Nasrallah said.
"If we are forced to use them to protect our people and our country, we will not hesitate to do so... and that will turn the lives of hundreds of thousands of Zionists into a living hell," he said in a speech marking al-Quds [Jerusalem] Day.
Nasrallah warned that any conflict would involve "tens of thousands of deaths".
He also said that if Israel were to undertake any military action over Iran's controversial nuclear programme, "the response will be enormous".
Any such action would present Iran with "the opportunity it has been dreaming of" since it was founded in 1979, he said.
Last month, an Israeli general warned that the Israeli military would respond "decisively" to any rocket attacks aimed at Tel Aviv.
"If we get to another war, Israel will hit Hezbollah decisively, quickly, as fast as we can in order to stop the fire from Lebanon to Israel," Brigadier General Herzi Halevi, commander of the country's northern division, said at a briefing.
He also said that towns in southern Lebanon used as launching bases for Hezbollah rocket attacks would be "destroyed".
Israel and Lebanon are officially in a state of war, and the former fought a devastating war with Hezbollah in 2006.
Iranian President Ahmadinejad, speaking in Tehran, said that Israel was a "cancerous tumour" that would one day cease to exist.
"Open your ears: there will be no Zionist regime and no United States [domination] in the new Middle East map," Ahmadinejad said.
"The occupied territories should be fully returned to the Palestinians," the Iranian president told supporters at Tehran University. "Nobody in the world can say he is in favour of human rights and approve the Zionist regime."
In Bahrain, meanwhile, police personnel clashed with protesters who attempted to hold their annual rallies marking al-Quds day. Several people were injured and others were arrested, after police fired teargas, stun grenades and birdshot rounds.
The marking of al-Quds Day is a show of support for Palestinians over the disputed holy city of Jerusalem. It is an annual event first introduced in Iran by Ayatollah Ruhollah Khomeini, the late supreme leader of Iran, in 1979.
Nasrallah also spoke on Friday of the uprising in Syria, saying that leaders of Muslim-majority countries such as Turkey and Saudi Arabia were not doing enough to end the bloodshed there.
Lebanon travel warnings
Meanwhile, the governments of the United States and Turkey have asked their citizens to avoid non-essential travel to Lebanon, after a series of kidnappings in the country linked to the uprising in Syria.
"The US embassy has received reports of an increased possibility of attacks against US citizens in Lebanon," the embassy said in a statement.
"Possible threats include kidnapping, the potential for an upsurge in violence, the escalation of family or neighbourhood disputes, as well as US citizens being the target of terrorist attacks in Lebanon."
The embassy also announced the suspension of the State Department's flagship Fulbright and English Language Fellow programmes in Lebanon, cutting short research projects and teaching grants for US university students and educators in Lebanon.
The Turkish foreign ministry issued a similar warning on Friday.
"It is deemed beneficial if our citizens avoid travelling to Lebanon unless absolutely necessary," said the ministry in a statement.
The warning came after around 20 people, including one Turkish national, were taken hostage in Beirut on Wednesday and another Turkish national on Thursday, according to the ministry.
Ankara said that it was continuing efforts at a multilateral level for the release of the two kidnapped citizens.
Several Gulf countries have ordered their nationals to leave the country immediately in the face of threats, particularly against Saudis and Qataris whose governments are staunch opponents of the Syrian regime.
On Friday, the International Committee for the Red Cross (ICRC) sought to relieve tensions by saying that it would aid the Lebanese Miqdad clan, who has carried out the kidnappings in response to the kidnapping of one of its members, in the search for the missing person.
"We have our group of Free Syrian Army hostages and don't intend to take any more. But if our relative Hassan is killed in Syria, the first to be executed will be the Turk," warned spokesman Maher al-Miqdad.
Hezbollah chief Nasrallah said his group was not responsible for the response to the abduction of the Lebanese Shias in Syria.
"What happened was beyond the control of Hezbollah and [the] Amal [movement]," he said,
On Friday, the Lebanese army said it was stepping up security at religious sites and other public places ahead of the Muslim festival of Eid al-Fitr, in response to the tense security situation.