An Israeli Merkava tank takes part in a military maneuver simulating an armed conflict with Iranian-back Hezbollah at an unspecified location near the Israeli-Syrian border on Sept. 6, 2017. (Atef Safadi/European Pressphoto Agency)

Syria accused Israel on Thursday of bombing a military site that has been linked to the production of chemical weapons, as well as missiles bound for the Hezbollah militant group, marking an escalation of cross-border incursions by Israeli jets.

Syria’s army command said the attack occurred at 2:42 a.m. near the western town of Masyaf, which military analysts say hosts a branch of the government agency responsible for developing and producing unconventional weapons and precision missiles. Syria said two soldiers were killed when missiles were fired from Lebanese airspace. It warned of “serious repercussions of such acts of aggression on the security and stability of the region.”

Israel has previously struck weapons convoys it has suspected of carrying arms to Hezbollah, a Lebanese Shiite militia that is fighting in Syria in support of the government of President Bashar al-Assad. Israel has said repeatedly that it sees the transfer to Hezbollah of advanced weaponry such as guided rockets as a red line.

But tensions along Israel’s northern borders with Lebanon and Syria have significantly sharpened in recent weeks, as Israeli Prime Minister Benjamin Netanyahu has accused Iran, Hezbollah’s main backer, of building facilities in Syria and Lebanon to produce precision-guided missiles. He has said that Israel cannot accept such activity.

Israel has watched nervously in recent years as the tide of the Syrian civil war has shifted in favor of Assad and as Iran and Hezbollah have become increasingly entrenched on the other side of the border.

In a meeting with Russian President Vladimir Putin last month, Netanyahu said Israel was prepared to act alone to curb Iranian expansion in Syria. Israel has stoutly opposed a cease-fire in parts of Syria, brokered by the United States and Russia, on grounds that the pact does not do enough to keep Iran and its proxies away from Israel’s borders.

The Syrian Observatory for Human Rights, a Britain-based monitoring group, said that a military storage camp next to the research center near Masyaf was used to store surface-to-surface rockets and that personnel from Iran and Hezbollah had been seen there more than once.

Maj. Gen. Yaakov Amidror, a former national security adviser to Netanyahu, said Hezbollah had received rockets from the production facility in the past.

“It’s another level of interference,” he said in a conference call, saying it was the first time that Israel had targeted a research-and-development facility. Israel has carried out nearly 100 strikes in Syria since the beginning of the civil war there, the Israeli air force chief told local media last month.

An Israel Defense Forces spokesman declined to comment on the latest strike.

A U.S. official, speaking on the condition of anonymity to discuss the situation freely, confirmed that the Israelis carried out the strike. The United States had no involvement in it and was assessing the situation, the official said.

Israel estimates that Hezbollah has a stockpile of more than 150,000 rockets, but it is concerned that Iran will help boost the group’s capacity to build more-accurate precision missiles.

In 2006, Israel fought a bloody month-long war with Hezbollah, whose founding mission is to fight Israel. In that conflict, Hezbollah fired more than 4,000 rockets into Israel, and Israeli jets devastated areas of southern Lebanon.

The attack Thursday may be a signal to Russia and the United States that Israel wants its security interests taken into account, Amos Harel, an Israeli defense analyst, wrote in the newspaper Haaretz. Amid deep disgruntlement over the cease-fire in Syria, Israel is saying that “we’re capable of disrupting the process of a future settlement in Syria if you insist on leaving us out of the picture,” he wrote.

As tensions on its northern border rise, Israel is carrying out its biggest military exercises in nearly two decades, involving about 30,000 troops who are simulating a ground invasion against Hezbollah in Lebanon.

Amidror said that the strike at the Syrian research center could lead to an escalation and that Israel’s armed forces should be “prepared.” Analysts say that although it is unlikely that either Hezbollah or Israel wants an all-out war, a conflagration could develop as Israel tries to limit Iran’s and Hezbollah’s expansion in Syria.

“Now it’s important to keep the escalation in check and to prepare for a Syrian-Iranian-Hezbollah response and even opposition from Russia,” Amos Yadlin, executive director of Tel Aviv University’s Institute for National Security Studies and a former Israeli military intelligence chief, wrote on Twitter. He described the facility as a “military-scientific center” that develops precision missiles, “among other things.”

In April, the U.S. Treasury Department imposed sanctions on 271 employees of the Syrian government agency responsible for chemical weapons production, weeks after a nerve agent was used to kill 83 people and injure dozens in the opposition-held town of Khan Sheikhoun.

On Wednesday, U.N. investigators formally accused the Syrian government of involvement in that attack and 20 others, most of them targeting civilians.

Morris reported from Jerusalem. Dan Lamothe in Washington contributed to this report.

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