Israel warned on Saturday that Iran would suffer the "consequences for choosing to escalate the situation any further" as fears grew of wider conflict more than six months into Israel's war against Hamas militants in the Gaza Strip.
The strong warning came after Iran seized a container ship linked to Israel in the Gulf, and the United States announced it was sending more troops to the troubled region.
The White House has repeatedly warned Tehran against carrying out a potentially imminent attack on Israel in response to an air strike on an Iranian diplomatic building in Damascus earlier this month.
Tehran has vowed to avenge the April 1 strike -- which killed 16 people, including two Iranian generals, and has been widely blamed on Israel -- but has not specified how.
Iran's Revolutionary Guards seized a container ship "related" to Israel in the Strait of Hormuz on Saturday, which was now heading towards Iranian waters, state media reported.
The ship's operator, the Italian-Swiss group MSC, said it was working with the relevant authorities to ensure the wellbeing of the 25 crew onboard.
Not long after the seizure was announced, Israeli military spokesman Daniel Hagari said that "Iran will bear the consequences for choosing to escalate the situation any further".
An adviser to Iran's supreme leader said that Israel was in "complete panic" over Tehran's looming response.
"They don't know what Iran wants to do, so they and their supporters are terrified," senior adviser Yahya Rahim said.
- Israel teen found dead -
The Gaza war began with Hamas's unprecedented October 7 attack against Israel which resulted in the deaths of 1,170 people, mostly civilians, according to Israeli figures.
Israel's retaliatory offensive has killed at least 33,686 people in Gaza, mostly women and children, according to the territory's health ministry.
The toll rose by 52 over the last 24 hours, the ministry said.
Israel's military said it had struck more than 30 Hamas targets across Gaza over the previous day.
In the main central city of Deir al-Balah, fire burned in the rubble of a destroyed mosque.
Israel's military "demanded that the whole area be evacuated" before it was "wiped out in minutes", said Abdullah Baraka, a witness.
In nearby Nuseirat refugee camp, Abd Thabet said residents had been warned to evacuate on Friday evening ahead of a large explosion that caused "massive destruction".
"All of the houses were demolished, including my home," the 35-year-old told AFP.
"There are children, women and the elderly, and we left without anything with us from our homes."
Tensions have also flared in the Israeli-occupied West Bank, where a missing Israeli teenager was found dead on Saturday.
Prime Minister Benjamin Netanyahu called the death of 14-year-old Benjamin Achimeir a "heinous murder".
After the boy went missing near the city of Ramallah on Friday, hundreds of Jewish settlers backed by Israeli forces raided nearby Palestinian villages, torching cars and homes, leaving at least one villager dead and dozens injured.
After the body of the teenager was found, Israel's Defence Minister Yoav Gallant warned against Israeli citizens taking "revenge" for his death.
- Travel warnings -
Following Iran's retaliation threats, Israel said it was strengthening air defences and paused leave for combat units.
A US defence official in Washington said that "we are moving additional assets to the region to bolster regional deterrence efforts and increase force protection for US forces".
The Netherlands said that its embassy in Tehran and consulate in Arbil, Iraq, would remain closed on Sunday "in connection with the rising tensions between Iran and Israel".
France earlier warned its nationals against travelling to the region, while the US embassy in Israel said it was restricting the movements of its diplomats over security fears.
German airline Lufthansa said its planes would no longer use Iranian airspace, while its subsidiary Austrian Airlines made a similar move. Australian airline Qantas said its long-haul Perth-London flights would also avoid Iranian airspace.
Gaza truce talks which started on Sunday in Cairo have brought no breakthrough on a plan presented by US, Qatari and Egyptian mediators, which Hamas has said it was studying.
- Calls for more aid access -
Washington has also ramped up pressure on Israeli Prime Minister Benjamin Netanyahu to increase aid flows to Gaza where the United Nations warns of imminent famine.
Israel's military said an undisclosed number of aid trucks had been allowed to enter Gaza Thursday through a newly opened border crossing.
Despite repeated AFP requests for comment, Israeli authorities did not disclose the exact location of the new crossing.
The UN Security Council has said that "more should be done to bring the required relief given the scale of needs in Gaza."
During the October attack, Hamas militants seized about 250 hostages, 129 of whom Israel says remain in Gaza, including 34 the army says are dead.
By Mohammed Abed With Laurie Churchman In Jerusalem