The U.S., U.K. and France are among several countries urging their citizens to leave Lebanon as heightened tensions in the region spark fears of a widening Middle East conflict.

The U.S. Embassy in Lebanon called on citizens to book 鈥渁ny ticket available to them.鈥 Britain鈥檚 Foreign Secretary David Lammy said his message for British citizens was 鈥渓eave now.鈥

The region is on high alert after Iran vowed revenge on Israel, who it blames for the assassination of Hamas鈥 political leader Ismail Haniyeh in the capital Tehran earlier this week. Haniyeh鈥檚 death came just hours after an Israeli strike on the Lebanese capital Beirut killed Hezbollah鈥檚 most senior military commander, Fu鈥檃d Shukr.

The developments have raised concerns that Israel鈥檚 war in Gaza, which is now well into its ninth month, could spill over into a full-blown Middle Eastern conflict.

It is thought that Lebanon-based Hezbollah could play a prominent part in any such retaliation. The militant group has been involved in daily exchanges of fire with Israel; overnight on Saturday Hezbollah fired 30 projectiles, most of which were intercepted by Israel.

Many countries already had travel warnings in place but have issued fresh advice in the wake of the latest developments.

France told its citizens to make arrangements to leave Lebanon 鈥渁s soon as possible鈥 in a statement from the Ministry for Europe and Foreign affairs on Sunday.

Jordan issued a similar warning to its citizens. The country was involved in shooting down Iranian drones when Iran launched unprecedented retaliatory strikes in April for a suspected Israeli attack on a diplomatic complex.

Iran鈥檚 state news agency (IRNA) reported that the Foreign Minister of Jordan will make a rare visit to the Iranian capital Tehran on Sunday, to 鈥渕eet and exchange views with Iranian officials regarding bilateral, regional and international issues.鈥

Airlines including Air France, Lufthansa and Kuwaiti Airlines have already cancelled flights to and from Lebanon while others diverted flights away from the country.

In a further sign of the region bracing for an Iranian retaliation, the U.S. on Saturday sent a carrier strike group, a fighter squadron and additional warships to the Middle East. It marked perhaps the largest movement of U.S. forces to the region since the early days of the Gaza war, when the Pentagon sent two carrier strike groups toward the Middle East in a very public warning to regional militant groups not to expand the fighting.

White House deputy national security adviser Jon Finer said Sunday that the U.S. and Israel are preparing for 鈥渆very possibility鈥 after the Pentagon sent the additional military assets.

鈥淲e and our ally Israel are preparing for every possibility. And that鈥檚 the vein in which the announcements made by the Pentagon took place. All of those posture adjustments are to prepare for a potential response against Israel from Iran or any other adversary,鈥 Finer told CNN鈥檚 Dana Bash on 鈥淪tate of the Union.鈥

Israelis have been stocking up on supplies, while a file from the Jerusalem municipality advised residents to 鈥渃lean and prepare their bomb shelters,鈥 warning they must be able to reach shelters in 90 seconds.