The airstrikes on Yemen's port of Hodeidah were a response to Houthi missile attacks on Israel in recent days, Israel said, amid fears that Middle East fighting could spin out of control and draw in Iran and the United States, Israel's main ally.
The Houthi-run health ministry said at least four people were killed and 29 wounded.
The strikes took place as Israel attacked more targets in Lebanon, where its intensifying bombardment over two weeks has killed a string of top Hezbollah leaders and driven hundreds of thousands of people from their homes.
Lebanon's Health Ministry said Israeli strikes on Sunday had killed at least 105 people, including 32 in Ain Deleb in the south and 33 people in Baalbek-Hermel in the northeast, and that 14 medics had been killed in air strikes over the past two days.
Israel on Sunday vowed to keep up its assault.
"We need to keep hitting Hezbollah hard," Israel's military chief of staff Herzi Halevi said.
Israeli drones hovered over Beirut overnight and for much of Sunday, with the loud blasts of new airstrikes echoing around the Lebanese capital.
Hezbollah and Israel have been trading fire across the border since the start of the war in Gaza, which was triggered by the Oct. 7 attack by Hamas. Yemen's Houthis have launched sporadic attacks on Israel throughout that time and disrupted Red Sea shipping.
Israel rapidly ramped up its attacks on Hezbollah two weeks ago, killing much of the group's leadership, as it aims to make its northern areas safe for residents to return to their homes. Israel's defense minister is now discussing widening the offensive.
Nasrallah's death dealt a particularly significant blow to the group he led for 32 years, and it was followed by new Hezbollah rocket fire on Israel. Iran said his death would be avenged.
The United States has urged a diplomatic resolution to the conflict in Lebanon but has also authorised its military to reinforce in the region.
U.S. President Joe Biden, asked if an all-out war in the Middle East could be avoided, said “It has to be." He said he will be talking to Israeli Prime Minister Benjamin Netanyahu.
U.S. Senator Mark Kelly said the bomb that Israel used to kill Nasrallah was an American-made 2,000-lb (900-kg) guided weapon.
In Iran, senior figures mourned the death of a senior Revolutionary Guards member killed alongside Nasrallah, and Tehran called for a U.N. Security Council meeting on Israel's actions.
Iranian Supreme Leader Ayatollah Ali Khamenei was moved to a secure location in Iran after Nasrallah's killing, sources told Reuters.
LEBANESE DEATHS
Nasrallah's body was recovered intact from the site of Friday's strike, a medical source and a security source told Reuters. Hezbollah has not said when his funeral will be held.
Nasrallah made Hezbollah into a powerful domestic force in Lebanon and helped turn it into the linchpin of Iran's network of allied groups in the Arab world.
Some Lebanese mourned him on Sunday.
"We lost the leader who gave us all the strength and faith that we, this small country that we love, could turn it into a paradise," said Lebanese Christian woman Sophia Blanche Rouillard, carrying a black flag to work in Beirut.
Lebanon's Health Ministry said more than 1,000 Lebanese have been killed and 6,000 wounded in the past two weeks, without saying how many were civilians. The government said a million people - a fifth of the population - have fled their homes.
In Beirut, some displaced families spent the night on the benches at Zaitunay Bay, a string of restaurants and cafes on Beirut's waterfront. On Sunday morning, families with nothing more than a duffle bag of clothes had rolled out mats to sleep on and made tea for themselves.
"You won't be able to destroy us, whatever you do, however much you bomb, however much you displace people - we will stay here. We won't leave. This is our country and we're staying," said Francoise Azori, a Beirut resident jogging through the area.
The U.N. World Food Programme began an emergency operation to provide food for those affected by the conflict.
Saudi Arabia and France said they were sending medical aid.
ISRAEL MILITARY ACTION
Israel's military said it struck dozens of targets in Lebanon including launchers and weapons stores and had intercepted eight projectiles coming from the direction of Lebanon and one from the Red Sea.
It also said dozens of Israeli aircraft had attacked power plants and Ras Issa and Hodeidah ports in Yemen, accusing the Houthis of operating under Iran's direction and in cooperation with Iraqi militias.
Israeli Defense Minister Yoav Gallant said: "Our message is clear - for us, no place is too far".
Nasrallah's death capped a traumatic fortnight for Hezbollah, starting with the detonation of thousands of communications devices used by its members. Israel was widely assumed to have carried out that action.
Hezbollah's arsenal has long been a point of contention in Lebanon, a country with a history of civil conflict. Hezbollah's Lebanese critics say the group has unilaterally pulled the country into conflicts and undermined the state.
However, Lebanon's top Christian cleric, Maronite Patriarch Bechara Boutros Al-Rai, said Nasrallah's killing had "opened a wound in the heart of the Lebanese". Rai has previously voiced criticism of the militia.
