AMMAN, Jordan — Jordan and Lebanon moved aggressively Monday to squelch the spread of violence from Syria’s deadlocked civil war, the most significant register yet of alarm over the fighting spilling over Syrian borders.
Islamic extremists attacked Jordanian soldiers on the border with Syria, killing a corporal, hours after Jordan’s government announced that it had foiled a major terrorist plot against foreign diplomats and tourists, officials said Monday.
Samih Maayta, the Jordanian communication minister, said eight militants attacked a military position with heavy arms Sunday night. In the ensuing gunfight, Corporal Mohamad Abdulla Manaseer Abbadi became the first member of Jordan’s military to be killed in action related to Syria’s civil war.
The Associated Press reported that the militants, whose nationalities Maayta did not provide, were trying to enter Syria illegally to join the rebel forces fighting President Bashar Assad’s regime. Maayta described them as extremist Salafis, a group banned in Jordan that promotes an ultraconservative brand of Islam.
Two hours after the attack, an additional five men suspected of ties to Al Qaeda tried to penetrate the border and clashed with soldiers, Maayta said. One was severely injured, but there were no Jordanian casualties. All 13 involved in both attacks were arrested.
On Sunday, the government said it had arrested a group of 11 Jordanians who had obtained explosives and other weapons from Syria that they intended to use in simultaneous assaults on civilian and government targets, including malls and the US Embassy.
Together, the episodes are the latest signs of how the chaos in Syria is destabilizing its neighbors.
Jordan, an important US ally, has increasingly aligned itself with Syrian rebel forces, delivering humanitarian aid to rebel-held cities and hosting about 200,000 Syrian refugees.
In Lebanon on Monday, troops launched a major security operation to open all roads and force gunmen off the streets, trying to contain an outburst of violence set off by the assassination of Brigadier General Wissam al-Hassan, a top intelligence official who was a powerful opponent of Syria. Lebanese tanks and armored personnel carriers rolled into the streets of Beirut and the northern Lebanese city of Tripoli to stop a night of gunfights.
Lebanese opponents of Syria have blamed the regime in Damascus for Hassan’s killing in a Beirut car bombing on Friday. With Lebanon already deeply divided over the civil war next door, the assassination has threatened to renew the kind of sectarian strife that raged there for decades.
Most of Lebanon’s Sunnis have backed Syria’s mainly Sunni rebels, while Lebanese Shi’ites tend to back Assad.
An unknown number of foreign Islamists have been fighting in Syria alongside the rebels. The Salafi movement has sent several fighters into Syria in recent months and Jordanian border patrols have caught others.
Efforts by Lakhdar Brahimi, the UN and Arab League envoy for Syria, to arrange a brief cease-fire seemed to dim Monday.
Syria’s state-run news agency SANA said Damascus supports the truce proposal but would not commit to halting fire during a four-day Muslim holiday until Western countries and their Gulf allies stop supporting rebels and halt their weapons supplies to the antiregime fighters.
Brahimi met with Assad in Damascus Sunday as part of his push for a cease-fire between rebels and government forces for the Eid al-Adha holiday, which begins Friday.
SANA said Assad told Brahimi that he supported his effort, but that any political solution to the conflict must be ‘‘based on the principle of halting terrorism.’’ Syria blames the war on foreign terrorists and governments that have been supplying the Syrian rebels.
The UN peacekeeping chief, Herve Ladsous, said Monday that the United Nations is already planning for a peacekeeping force in Syria should the cease-fire take hold.
The mission would require a Security Council mandate. Ladsous said it is still too early to say how many peacekeepers might be deployed.
‘‘It’s a shocking fact that every day 150 to 200 civilians are killed, and it has almost become part of the background noise and it is simply unacceptable,’’ Ladsous said.