“There is now so much friction between the sides that it is very natural that a single miscalculation across the board on one of these flash points could spiral out of control,” said Ali Vaez, director of the Iran Project at the International Crisis Group.
Amplifying these tensions, he said, was the looming May 12 deadline by which President Trump has said he will decide whether to pull the United States out of the international agreement to curb Iran’s nuclear program.
Iran has sought to preserve the deal, which gives it significant sanctions relief, while the United States’ regional allies have campaigned to have it scrapped to punish Iran for what they see as its destabilizing activities across the Middle East.
They appear to have clear support from the Trump administration in their efforts to confront Iran.
On a phone call hours before Sunday’s strike, Mr. Trump spoke by phone with Prime Minister Benjamin Netanyahu of Israel about “the continuing threats and challenges facing the Middle East region, especially the problems posed by the Iranian regime’s destabilizing activities,” according to a statement from the White House.
The new secretary of state, Mike Pompeo, who was visiting Israel at the time, said in a news conference with Mr. Netanyahu that American coordination with its allies was “critical to our efforts to counter Iran’s destabilizing and malign activities throughout the Middle East.”
“The United States is with Israel in this fight, and we strongly support Israel’s sovereign right to defend itself,” Mr. Pompeo said.
But it was not clear whether American officials were informed before the strikes took place.
The rivalry between Iran and its regional rivals cuts across the Middle East, from Lebanon and Syria to Iraq, Yemen and the Persian Gulf.
Analysts say that Iran, which has few powerful allies and shares a region with hostile countries that spend much greater sums on their militaries, has instead built relationships with proxy forces that can fight on its behalf. These include Hezbollah, the Lebanese militant group and political party; a variety of Shiite militias in Iraq; and the Houthi rebels in Yemen.
This network allows Iran to project military strength abroad while deterring potential attacks on its homeland from Israel and Saudi Arabia.
Iran’s enemies argue that these activities increase instability in the region by undermining state structures and empowering militias that operate above the law.
In recent years, Iran’s greatest investments have been in Syria, where it has sent military officers to help preserve the government of President Bashar al-Assad. Israel accuses Iran of using the cover of the war to build a military infrastructure there that could be used in a confrontation with Israel.
Throughout the war, Israel has frequently struck convoys believed to be carrying weapons to Iran’s regional allies. In April, these attacks escalated. It first launched strikes on a Syrian military base, killing seven Iranians, including a top official in Iran’s drone program.
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Sunday night’s attack appeared to be a further escalation, with a higher death toll.
The Syrian Observatory for Human Rights, which is based in Britain but monitors Syria through contacts there, said that the attacks killed at least 26 people, most of them Iranians.
The strikes hit munitions warehouses at the 47th Brigade military base in central Hama Province that Iran and its proxies used, destroying ground-to-ground missiles and causing large explosions, the observatory said.
The blast was large enough that it was picked up by earthquake monitors. The European-Mediterranean Seismological Center reported a disturbance in the area of the base with a magnitude of 2.6, it said, equivalent to a minor earthquake.
Other reported attacks struck a fire station, also in Hama Province, and the Neirab military air base near Aleppo. But no deaths or significant destruction was reported that those sites.
An official from the regional alliance that includes Iran, Syria and Hezbollah confirmed that the strikes near Hama had hit a storage site on the base and said they had destroyed 200 missiles and killed 16 people, including 11 Iranians. The official spoke on the condition of anonymity because he was not authorized to speak to journalists.
Neither Israel nor Iran appeared interested in publicizing the strike, which analysts said was probably an effort to diminish the chances that Iran would feel the need to retaliate immediately.
Israel’s military does not comment on individual attacks in Syria, and a spokesman declined to comment on Sunday’s attack, most likely because if Israel claimed responsibility it could put pressure on Iranian leaders to strike back. Israel’s security cabinet convened an emergency meeting on Monday, apparently to discuss the rising tensions with Israel’s northern neighbors.
A semiofficial Iranian news agency, ISNA, initially said that 18 of 40 people killed in the attacks were Iranian, but the report was later taken down and Iranian officials denied that any of their people had been killed.
That, too, could have been so that Iranian leaders would not feel compelled to respond immediately, said Amos Yadlin, the former director of intelligence for the Israeli military and now executive director of the Institute for National Security Studies in Tel Aviv.
“If there are no Iranian casualties, you are not committed to retaliation,” Mr. Yadlin said in a conference call with reporters on Monday.
But he said he expected that Iran would eventually respond to the April attacks, although it was not clear when, where or how.
“The Iranian retaliation is on its way,” he said.
Mr. Vaez, the analyst, said that his recent conversations with Iranian officials also suggested that Iran would eventually retaliate for Israel’s strikes on Iranian assets in Syria.
“They believe that this is a slippery slope, that there is a need to send a message to Israel that there is a cost associated with its pushing the envelope too far,” he said.
But influencing their decision on when to respond was their concern that any action taken now could push Mr. Trump toward withdrawing from the nuclear agreement, Mr. Vaez said, adding that Israel’s decision to strike on Sunday might have been intended to provoke an Iranian response for that very purpose.
“We are in a vicious cycle, and the reality is that the collapse of the nuclear deal will significantly increase all these tensions,” Mr. Vaez said. “All the parties will take the gloves off at that stage.”