Secretary of State John Kerry said Wednesday that the United States was increasingly concerned that the escalating fighting in Syria might slip across the border withLebanon and destabilize that country.
“We’re deeply concerned about this spilling over into Lebanon,” said Mr. Kerry, who came to Jordan to attend an 11-country meeting on the deteriorating situation in Syria.
Lebanon, Mr. Kerry added pointedly, is “at risk.”
The decision by Hezbollah, the Lebanese militia and Iranian ally, to join the battle for the strategic city of Qusayr in Syria, and the prospect that the Syrian rebels might respond by carrying the fight to Hezbollah operatives in Lebanon, has alarmed the Obama administration.
Mr. Kerry said that several thousand Hezbollah members were operating in Syria. Members of Iran’s paramilitary Quds force and Iraqi Shiite militia members, some of whom have been encouraged by Iran to fight in support of the government of Bashar al-Assad, are also in Syria, other American officials said, who like several other United States officials quoted spoke on the condition of anonymity.
The White House has been increasingly concerned that the fierce fighting in Qusayr and the sectarian violence in the northern Lebanese city of Tripoli will lead to a wider regional conflict.
President Obama called the president of Lebanon, Michel Suleiman, on Monday to urge the Lebanese armed forces to prevent the flow of Hezbollah fighters and weapons across the border into Syria. But Mr. Suleiman, a Christian, has little influence over Hezbollah and its fighters.
“We don’t want to see any escalation or spread of this war to Lebanon,” said a senior Obama administration official. “Lebanon is facing enough challenges with nearly 500,000 official refugees and nearly one million Syrians in a country of four million. The last thing it needs is sectarian violence in Lebanon itself.”
Americans officials have also conveyed their worries to the Supreme Military Council or S.M.C., the military wing of the Syrian opposition that is led by Gen. Salim Idris, and urged it not to chase fighters across the border into Lebanon.
“We will continue to urge them not to get involved in Lebanon, but the pressures are there, and even beyond the S.M.C. itself, there are Sunnis and Syrians who might not abide by that,” the senior administration official said.
He added that the United States might condition its promise of increased nonlethal aid to the rebels on their willingness not to strike in Lebanon.
While the United States may have leverage with General Idris, it has no ability to control some jihadists — like the Nusra Front, which is also fighting Syrian government forces.
A senior State Department official in Amman said that Syrian opposition commanders in the Homs area had reported that arms and other military supplies had been making their way to Hezbollah operatives in Syria from Lebanon’s Bekaa area.
“We have said that we need to keep Lebanon out of this and we need to find ways to stop the flow coming out of Lebanon,” the State Department official told reporters here, reprising the United States message to the Syrian opposition.
General Idris grew up in a village near Qusayr, making the battle there a personal matter.
“They are invaders. They are dogs acting like beasts,” he said in an interview, referring bitterly to the Hezbollah fighters. “I swear to god, Hassan Nasrallah will pay the price,” General Idris added, referring to the Hezbollah leader.
But General Idris also asserted that the rebels did not want to impinge on Lebanon’s sovereignty.
The concern over Lebanon was just one issue at the meeting here that brought together foreign ministers and leading members of the Syrian opposition.
The main point of the meeting was to set the stage for an expected international conference in Geneva next month that is intended to facilitate negotiations between the Assad government and the Syrian opposition over the possible establishment of a transitional government.
A number of outstanding issues remain, including who in the Syrian opposition might be willing attend and Iran’s role in any future diplomatic discussions.
The planning for the Geneva meeting also comes as the Assad government has been making gains on the battlefield and the leverage of the United States and its partners to induce Mr. Assad to vacate his post appears to have declined.
“Yeah, he’s made a few gains in the last days,” Mr. Kerry said during his news conference, referring to Mr. Assad. “But this has gone up and down in a seesaw.”
Mr. Kerry asserted that any progress the Syrian government had made in the war would prove to be ephemeral. He warned that the United States and its partners were prepared to increase support for the Syrian opposition if Mr. Assad refused to negotiate an end to his rule and agree to the establishment of a transitional government.
If Mr. Assad is not prepared to negotiate in “good faith,” Mr. Kerry said, “we will also talk about our continued support and growing support for the opposition in order to permit them to continue to be able to fight for the freedom of their country.”
It remains unclear whether that warning will register with Mr. Assad. It took two months for the United States to send the food rations and medical kits to the opposition that it promised in late February. And the Obama administration has not yet sent the additional nonlethal aid to the opposition that Mr. Kerry said in late April would be forthcoming.
At the same time, Russia has been providing the Assad government with arms, as has Iran, according to American officials.
At the 11-country meeting, General Idris briefed the delegates on the military situation. George Sabra, the acting head of the Syrian opposition, also attended. The Syrian opposition is in the process of picking new leaders and that has slowed its decisions on who from its ranks might attend the Geneva session.
A communiqué issued at the end of the meeting in Amman stressed the need for political negotiations at the Geneva meeting and promised “additional support” to the armed wing of the opposition. It also called for the immediate withdrawal of Hezbollah fighters, and fighters from Iran and other foreign countries.