BEIRUT, Lebanon -- The leader of Hezbollah, the powerful Lebanese militant group, escalated tensions with Israel on Thursday over the recent Israeli airstrikes near Damascus, suggesting that the Syrian government would respond by providing Hezbollah fighters with the weapons that Israel wants to keep out of their hands.
While the Hezbollah leader, Hassan Nasrallah, did not specify the type of arms, he said they were "unique weapons that it never had before" that would "change the balance" of power with Israel, which regards his group's alliance with Syria and Iran as one of its most potent security threats.
In a televised speech, Mr. Nasrallah said the transfer of the weapons would be Syria's "strategic response" to the airstrikes that hit the outskirts of Damascus on Sunday.
Israel has not publicly acknowledged responsibility for those strikes. But Israeli leaders have said they would take military action to prevent Hezbollah from obtaining "game changing" weapons like chemical arms, which Syria is believed to possess in large quantities, and sophisticated long-range missiles that could hit Israel from Hezbollah-controlled areas of southern Lebanon.
Analysts close to Hezbollah said they believed Mr. Nasrallah was referring in his speech to long-range missiles, not chemical munitions. But the Israelis have expressed growing concern about the possible use of chemical weapons in Syria's civil war, suggesting that the transfer of such weapons to groups hostile to Israel was more and more likely.
The Israeli airstrikes last Sunday -- far more powerful than two previous Israeli strikes that American officials said were aimed at consignments of long-range missiles en route to Hezbollah from Iran -- heightened fears that Syria's war could lead to a regional conflagration.
Syrian officials said Thursday that they would respond forcefully to any future Israeli attacks and that they were planning to retaliate for Sunday's strikes, possibly by authorizing Syria-based militant groups to attack in the Golan Heights, the disputed border region captured by Israel from Syria in the 1967 war.
Syria's deputy foreign minister, Faisal Mekdad, said in an interview with Agence France-Presse in Damascus that any new Israeli attack would bring a "harsh and painful" response from Syria's military.
"Instructions were given to respond immediately to any Israeli attack," he said in the interview, which was also published on the Web site of Press TV, an Iranian satellite channel. "Syria will not allow this to be repeated."
President Bashar al-Assad of Syria told recent visitors to Damascus that his government had decided to give Hezbollah "everything," according to an article in the Lebanese pro-Hezbollah newspaper Al-Akhbar. He also said that Syria plans to become "a resistance country" and take a more active role in opposing Israel.
Syria has long positioned itself as the champion of the Palestinian cause and as Israel's greatest Arab foe, but since 1973 it has rarely clashed militarily with Israel.
The escalating tensions with Israel came as the United States was seeking to exert more diplomacy in conjunction with Russia, Syria's most powerful foreign supporter, aimed at starting negotiations to settle the Syrian conflict.
Secretary of State John Kerry, asked about intelligence reports that Russia was completing a sale of surface-to-air missiles to Syria, told reporters the focus should be on the Russian-American agreement to convene peace talks as soon as possible.
Mr. Kerry announced that agreement on Tuesday after consultations in Moscow with President Vladimir V. Putin and Foreign Minister Sergey V. Lavrov.
"I had my say with President Putin, and I had my say with Sergey Lavrov, and we made an agreement to go to the negotiations in the next days," Mr. Kerry said in Rome, where he was holding further talks on Syria. "And I'm not going to get into -- here, not, at this moment, as I said -- distinguishing features between one country's aid and another country's aid, and who is doing what," he said. "That would be counterproductive to what we're trying to accomplish."
He added that the United States had "made it crystal clear that we would prefer that Russia not supply assistance" to Syria's air defenses because of the threat it posed to the region, particularly Israel.
In addition to meetings with Italy's new prime minister and foreign minister, Mr. Kerry discussed Syria with Jordan's foreign minister, Nasser Judeh, pledging $100 million in new humanitarian assistance, nearly half of it to help Jordan deal with a flood of refugees from the fighting. He also spoke by telephone with the United Nations secretary general, Ban Ki-moon, in an effort to start negotiations.
Mr. Kerry suggested that the United Nations would soon announce a date for talks to begin, presumably in Geneva, where an effort to create a framework for a negotiated settlement began last year, only to stall as the fighting continued unrelentingly.
In Paris, the French foreign minister, Laurent Fabius, said in an interview with Le Monde that France favored the diplomatic solution advanced by Mr. Kerry, but that it also wants to rethink the European Union arms embargo in order to help the Syrian rebels.
Mr. Fabius also proposed that the United Nations should declare Syria's Islamist Nusra Front a terrorist organization to differentiate it from other Syrian rebel groups.
The United Nations Security Council has already looked informally at whether to impose sanctions on the Nusra Front after it pledged allegiance last month to Al Qaeda. The State Department designated Nusra a terrorist organization in December, but the group has grown stronger since then; it is considered one of the Syrian insurgency's most effective fighting forces.
Senior French officials said that the French position has become noticeably more cautious in the last few weeks, especially since the resignation last month of Moaz al-Khatib, the leader of the main political opposition group, the Syrian National Coalition, amid political infighting.
French officials would like to see the opposition's main armed wing, the Free Syrian Army, become more centralized and come under the command of a civilian hierarchy before moving ahead with arms transfers, the officials said.
At the United Nations, where a deadlock in the Security Council has frozen any concrete action on Syria, Qatar and other supporters of the Syrian opposition began circulating a draft General Assembly resolution on Thursday strongly condemning the Assad government and calling for a political transition.
Such resolutions are nonbinding, but its backers hope a significant vote supporting the measure in the 193-member assembly as early as next week will put added pressure on Damascus to end the fighting.
In a related development, the United Nations said Thursday that Mr. Ban, the secretary general, had asked Lakhdar Brahimi to stay on as the special Syria envoy for both the United Nations and the Arab League and that he had agreed.
Mr. Brahimi had been expected to resign in frustration over the lack of progress on the political track. But he apparently changed his mind after the Russian-American agreement to convene a peace conference -- something Mr. Brahimi had long sought.
Reporting was contributed by Hwaida Saad from Beirut, Steven Erlanger from Paris, Steven Lee Myers from Rome, Neil MacFarquhar from the United Nations and Rick Gladstone from New York.
This article originally appeared in The New York Times.