BEIRUT — Suicide bombers struck the Iranian Embassy on Tuesday, killing 23 people, including a diplomat, and wounding more than 140 others in a “message of blood and death” to Tehran and Hezbollah — both supporters of Syrian President Bashar Assad.

The double bombing in a Shiite district of Beirut pulled Lebanon further into a conflict that has torn apart the deeply divided country, and came as Assad’s troops, aided by Hezbollah militants, captured a key town near the Lebanese border from rebels.

The bombing was one of the deadliest in a series of attacks targeting Hezbollah and Shiite strongholds in Lebanon in recent months.

An al-Qaida-linked group said it carried out the attack as payback for Hezbollah’s backing of Assad forces against the mainly Sunni rebels as the Syrian civil war increasingly becomes a confrontation between regional powers.

The Syrian army’s border offensive is part of a larger government push that started last month and has seen forces loyal to Assad firmly seizing the momentum in the war, taking one rebel stronghold after another.

The attacks raised fears in Lebanon that Islamic extremists, now on the defensive in Syria, would increasingly hit back in Lebanon. The country is suffering the effects of competing sectarian loyalties.

The midmorning explosions hit the neighborhood of Janah, a Hezbollah stronghold and home to several embassies and upscale apartments, leaving bodies and pools of blood on the glass-strewn street amid burning cars.

U.N. Secretary-General Ban Ki-moon condemned the attacks and called on all Lebanese to recognize that “such appalling and indiscriminate acts of violence” target everyone in the country, U.N. acting deputy spokesman Farhan Haq said.

U.S. Secretary of State John Kerry called the bombings “senseless and despicable,” and said “our hearts go out to the Iranian people after this violent and unjustifiable attack claimed the life of at least one of their diplomats.

The dead Iranian was identified as Ibrahim Ansari, a 54-year-old diplomat who took up his post a month ago and was overseeing regional cultural activities, said Iranian Ambassador Ghazanfar Roknabadi, speaking to Hezbollah’s Al-Manar TV from inside the embassy compound.

Also among the dead was Radwan Fares, a Lebanese national who headed the facility’s security, according to a Lebanese official at the embassy who spoke on condition of anonymity because he was not authorized to give official statements.