Saudi jets pounded neighboring Yemen on Thursday and Egyptian warships steamed toward its coast in the start of an Arab-led offensive against Shiite rebels that has become a showdown between the major powers in the Middle East.

Saudi Arabia and its Arab allies plunged into the Yemen crisis after Shiite insurgents, known as Houthis, pushed from their power base in the north into the south, forcing the country’s pro-Saudi, Western-backed president to flee.

The move inflamed the already tense relationship between Shiite power Iran, which has increased its support for the Houthis as their rebellion has expanded, and Saudi Arabia and other Sunni-dominated nations.

Some officials warned that the fight could escalate further. Saudi state TV said Thursday that a ground offensive was being studied but gave no further details. Egypt’s minister of foreign affairs, Sameh Shoukri, said in a speech to Arab foreign ministers that his country was willing “to send ground forces if necessary” to back the anti-Houthi fight.

Four Egyptian naval vessels were dispatched for Yemen, where they were expected to arrive late Thursday, according to official news media.

Ground forces would probably face stiff resistance from the Houthis, who have taken control of large swathes of Yemen and appear to have strong support from the country’s military and the powerful former president, Ali Abdullah Saleh.

In a televised speech, Houthi leader Abdulmalik al-Houthi predicted that Yemenis would oppose the “criminal, unjust and unjustified aggression” by Saudi Arabia.

But the military pressure could force the rebels back into power-sharing talks that collapsed in January, when the insurgents put President Abed Rabbo Mansour Hadi under house arrest after clashes­ in the capital. In February, the Houthis effectively toppled the government.

Saudi Arabia has mobilized a major force, suggesting that it was prepared for a sustained fight. Up to 10 countries are believed to be participating in the Saudi-led coalition, although many have refrained from acknowledging their role.

Bahrain said Thursday that it had responded to a Saudi call for assistance by sending 12 fighter jets. Jordan’s Petra News Agency, quoting unnamed “official” individuals, said that Jordan was also taking part in the offensive. The report did not describe Jordan’s aid, which is believed to consist of fighter jets. Sudan said it would join the operation, and Pakistan said its defense minister would visit Saudi Arabia on Friday to assess how it could help the kingdom.

The United States had viewed Hadi as a key partner in the fight against al-Qaeda, whose Yemen branch is considered especially dangerous. Washington has offered intelligence help and other logistical support to the current Saudi-led operation.

It was unclear how Iran would respond to the show of strength by Saudi Arabia and its allies. Iran’s foreign minister, Mohammad Javad Zarif, told Iran’s Arabic-language al-Alam channel that “we will spare no effort to contain the crisis in Yemen.” But the Reuters news agency quoted an unidentified senior Iranian official as saying that “military intervention is not an option for Tehran.”

According to Saudi-owned al-Arabiya News, Saudi Arabia has dedicated 100 fighter jets, 150,000 soldiers and navy units to the operation in Yemen.

Saudi officials have said they are seeking to restore Hadi to power. He was driven from his last outpost in the southern port of Aden on Wednesday. He resurfaced Thursday at an air base in the Saudi capital, Riyadh.

The head of the Arab League, Nabil Elaraby, and Egypt’s Shoukri announced Thursday during the meeting of Arab foreign ministers that the officials had decided to create a unified military force able to respond to crises. It was to be discussed further at an Arab Summit that is to begin Saturday in the Egyptian beach resort of Sharm el-Sheikh.

The air attacks in Yemen began early Thursday. Saudi fighter jets struck the main civilian airport and the Dailami air force base in Sanaa, which is under the control of the Houthis, hitting the runways and destroying four Yemeni air force planes. In the south, the invading forces pounded al-Anad military base, where about 100 U.S. Special Operations troops had been station until they pulled out last week.

There were also airstrikes in the northern province of Saada, apparently aimed at hitting the Houthi leader.

At least 23 people were killed in the attacks, according to a Yemen Ministry of Health official, who spoke on the condition of anonymity because he was not authorized to comment. They included six children and four women, he said. At least 47 people were wounded, he said.

“This morning was horrific. We woke up to the sounds of heavy shelling,” said Salah Mohammed, 35, an airline employee who lives near the airport. As explosions rang out, he said, he ran upstairs to bring his mother, sisters and children to safety.

“We all stayed in the hall downstairs as the heavy shelling and sounds of the anti­­aircrafts started to intensify. The electricity was off, and I had no idea what was going on. The children were crying, and we were all worried,” he said.

After the attacks subsided, he said, he went out to inspect the damage. At least six houses near the airport were destroyed, he said. “We reject such actions, and this is an invasion,” he said.

Other residents, however, said they were grateful that the Houthis were facing resistance.

“I oppose any foreign military interference,” said Osama Muhsin Alabdali, 34, a supervisor in a telecommunications company. “However, I am also glad that the Houthis are being stopped, especially since they started moving toward the south.”

Supporters of the Houthis joined a big protest in Sanaa on Thursday condemning the attacks. In Taiz, a south-central city recently seized by the Houthis, residents flocked to a demonstration supporting the offensive. Some carried signs saying “Thank you, Saudi Arabia,” according to images shown on regional TV.

Hadi’s government had appealed recently for military intervention from the Gulf Cooperation Council, which is anchored by the Saudis and includes Kuwait, Oman, the United Arab Emirates, Bahrain and Qatar.

According to the Egyptian state newspaper El Ahram, Egypt has sent four naval warships to the Red Sea via the Suez Canal. A military individual quoted anonymously by the paper stated that the naval vessels were going to “secure the theater” to maintain control of Egyptian territorial waters but that they were on alert “to intervene in any way deemed necessary by the armed forces.”

In Switzerland, Secretary of State John F. Kerry took time away from nuclear talks with Iran to join a telephone conference with the foreign ministers of the Gulf Cooperation Council. The U.S. government has had to significantly scale back its counterterrorism presence in Yemen because of the Houthi advances.

Meanwhile, financial markets reacted to the fast-moving events in Yemen, with many stock exchanges falling and global oil prices surging.

Saudi Arabia last launched military action in Yemen in 2009, conducting airstrikes against the Houthis near the Saudi border after it said its border guards had been fired upon.

Heba Habib in Cairo, Shaiq Hussain in Islamabad, Daniela Deane in London, and Brian Murphy and Karen DeYoung in Washington contributed to this report.