A bomb exploded at a crowded bus stop near Jerusalem’s main bus station on Wednesday, killing one woman and wounding at least 24 other people. It was the worst attack in Jerusalem in four years, putting Israelis on alert, shattering years of relative calm here and prompting international condemnation.

Paramedics and others aided the wounded Wednesday after an explosion at a crowded Jerusalem bus stop. One person was killed and at least 24 were wounded.

Residents ran for cover Wednesday during a rocket attack on the Israeli city of Beersheba, about 25 miles southeast of Gaza.

The blast came amid escalating tensions along Israel’s border with Gaza.

On Tuesday, stray Israeli mortar fire killed three Palestinian youths and a 60-year-old man as Israel responded to a rocket attack. Soon afterward, the Israeli Air Force killed four militants in a car in Gaza, all members of Islamic Jihad. The Israeli military said the men were preparing to launch more rockets at Israel.

On Tuesday night and Wednesday, Palestinian militants fired rockets deep into southern Israel, and Israel responded with airstrikes in Gaza. Early Thursday morning, Israeli warplanes struck smuggling tunnels along the border of Gaza and Egypt, and they also hit a power transformer, Reuters reported.

The spiraling violence pushed the already dim prospects of Israeli-Palestinian peace negotiations further away as talk in Israel turned to the need for firm action to restore the country’s security.

The prime minister of Israel, Benjamin Netanyahu, said certain elements had been “trying to test our resolve and the fortitude of our people.”

“They will learn that the government, the I.D.F. and the Israeli public have an iron will to defend the state and its citizens,” he said Wednesday evening as he was about to depart for Moscow, using the abbreviation for the Israeli Defense Forces. He added, “We will act vigorously, responsibly and prudently in order to maintain the quiet and the security that have prevailed here over the past two years.”

Islamic Jihad praised the Jerusalem bombing, as did the Popular Resistance Committees, another militant group that is considered close to Hamas, the Islamic organization that controls Gaza. No group immediately claimed responsibility for the attack.

The atmosphere began to change with the killing earlier this month of an Israeli family, including three children, by suspected Palestinian assailants in the West Bank settlement of Itamar. Israel criticized the more moderate Palestinian leadership in the West Bank at the time, accusing it of hesitating to condemn the murders and of indirectly encouraging violence by allowing incitement in its schools, mosques and news media.

Mahmoud Abbas, president of the West Bank-based Palestinian Authority, promptly condemned the Jerusalem bombing, as well as Israel’s deadly actions in Gaza, according to the official Palestinian news agency, Wafa.

Salam Fayyad, prime minister of the authority, which rivals Hamas, said in a statement Wednesday, “I condemn this terrorist operation in the strongest terms, regardless of which party stands behind it.”

The bomb detonated as two buses pulled into the crowded stop at the western edge of the city, near a convention center and the city’s main bus station. Yitzhak Aharonovitch, Israel’s minister of internal security, said the device was relatively small, weighing from two pounds to a little over four pounds. Witnesses said the explosion came from a rolling suitcase placed near a public telephone at the stop.

Small holes were seen in the body of one of the buses, suggesting that the explosive device had been packed with ball bearings to increase the level of damage.

“I knew instantly that it was a terrorist attack,” said Yair Zimmerman, a volunteer medic who was on one of the buses.

“I told the driver to move forward several meters and to open the door,” he said, speaking at Shaare Zedek hospital, where he and 13 others had been taken. “When I went out, I saw that a kid had been thrown six or seven meters. I saw four or five people lying on the ground badly hurt, including a woman in a pool of blood. There was a terrible smell of burned plastic and blood.”

The other wounded were taken to the Hadassah University Medical Center in Ein Kerem.

The woman who was killed suffered a chest injury in the blast and died a short time later, officials at Hadassah said. They could not provide any immediate information on her identity.

In the hours after the blast, the police were searching for a car they said had been seen fleeing the scene, and checkpoints were set up on roads across the country.

At the time of the explosion, Mr. Netanyahu was meeting with senior members of the security establishment for consultations about the situation along the border with Gaza. He was supposed to leave for Russia at 5 p.m. local time, about two hours after the explosion, but he delayed his departure by a few hours.

Israel’s defense minister, Ehud Barak, hinted that Israel was planning a response against Hamas in Gaza.

“We will not tolerate attacks on Israeli civilians, neither in the southern communities nor in Jerusalem,” he said in a statement soon after the bombing.

Two Katyusha-type rockets were fired at the southern Israeli city of Beersheba, about 25 miles southeast of Gaza, on Wednesday morning. One hit a street in the center of the city, slightly wounding one man and causing damage to nearby houses. On Tuesday night, a similar rocket fell just short of the Israeli port city of Ashdod, about 20 miles north of Gaza.

While militants in Gaza have fired a trickle of mortar shells and crude short-range rockets at southern Israel in recent months, longer-range rockets aimed at Israeli cities have been rare since an informal cease-fire went into effect in January 2009. The escalation began on Saturday when Hamas fired dozens of mortar shells at Israel in a 15-minute period.

Mr. Barak said that Israel held Hamas responsible for the latest rocket attacks, and added that “responsibility comes with a price.”

Another warning came from Amos Gilad, a senior Israeli Defense Ministry official and a retired general, who told reporters, “One lesson after our operation in Gaza for Hamas is that we could destroy them very easily as a response to murders and attacks carried out against us,” after a lull. “They are making dramatic mistakes if they think they can murder and terrorize.”

Defense Secretary Robert M. Gates, traveling in Egypt, called the Jerusalem bombing “a horrific terrorist attack,” The Associated Press reported. But, speaking of Israel, he said he “would not characterize the situation there as deteriorating.”

Two weeks ago, an Israeli municipal worker lost his hand when a pipe bomb exploded in a trash bag in the southern section of Jerusalem. The police have made no arrests in that case.