Overwhelmed by a massive influx of desperate refugees, Lebanon began imposing unprecedented visa restrictions on Syrians on Monday, including those fleeing their country's civil war.
"Today we began implementing the new entry measures and Syrians at the borders have begun presenting their documents to enter," a source at Lebanon's general security agency said.
The visa restrictions are the first in the history of the two countries and come as Lebanon struggles to deal with more than 1.1 million Syrian refugees.
The influx has tested the country's limited resources, as security has deteriorated.
For months, Lebanon's government has sounded the alarm, warning the international community it could no longer deal with the influx.
In October, Social Affairs Minister Rashid Derbas said Lebanon would stop accepting displaced Syrians, with exceptions on humanitarian grounds only.
He told AFP that the new visa requirement was intended to limit the flood of new arrivals.
"The goal is to prevent (Syrians) from taking refuge" in Lebanon, and "to more seriously regulate the entry of Syrians."
- 'High time' for restrictions -
Khalil Jebara, adviser to Lebanon's interior minister, said the country would continue to provide humanitarian exceptions, but that restrictions were needed.
"We respect our international obligations... we will not expel anyone and there will be humanitarian exceptions," he said.
"But it's high time to regulate the issue of Syrians entering Lebanon," he added.
"Their presence imposes a great security, economic and social burden on Lebanon, and pressure that the infrastructure can no longer take."
Washington acknowledged that the flood of refugees was a "tremendous challenge" for Syria's neighbours now hosting more than three million people, but said it was "very concerned" by the new visa requirements.
"We encourage the government of Lebanon to coordinate closely with the UN in the development of criteria to ensure those fleeing violence and persecution are able to cross into Lebanon," State Department spokeswoman Jen Psaki said.
"We will continue to strongly encourage the governments of the region to provide refuge... for asylum seekers."
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Unlike Jordan and Turkey, Lebanon declined to create refugee camps, meaning refugees are dispersed throughout the country.
It has also seen its fragile security situation deteriorate, with jihadists from Syria briefly overrunning Arsal -- a border town in eastern Lebanon hosting tens of thousands of refugees -- in August and kidnapping several dozen Lebanese police and soldiers.
A spokesman at Lebanon's general security agency said the measures would help track the huge refugee population, which the government estimates at 1.5 million people.
"We have a problem called 1.5 million Syrians and there is no magical solution for it, these measures are the first step," he said.
"It's a way to track Syrians... so we know where to find them."
UN refugee agency UNHCR has registered 1.1 million arrivals, but many more are thought to be in the country unregistered, and thousands have entered Lebanon through illegal crossings.
Lina Khatib, director of the Carnegie Middle East Centre think-tank, said the visa measures were a result of Lebanon's failure to implement a refugee policy early in the Syrian conflict.
Lebanon's government is divided between supporters of Syria's regime, including the powerful Shiite movement Hezbollah, and backers of the Syrian uprising, making agreement on refugees difficult.
- Spectre of Palestinian refugees -
Khatib said Lebanese concern about the refugee influx was "both real and exaggerated".
Wages have gone down and rents have increased, but Lebanese employers have exploited Syrians willing to work for lower wages, she said.
Lebanon is also marked by its experience with Palestinian refugees who fled their homes with the creation of Israel in 1948.
More than 400,000 Palestinians, mostly descendants of the original refugees, remain in squalid and largely lawless camps in Lebanon, and Palestinian armed groups are blamed by many Lebanese for sparking the country's 1975-1990 civil war.
Lebanon's complex sectarian make-up also plays a role -- most Syrian refugees are Sunni Muslims, like the Palestinian refugees before them, raising fears they could change the country's delicate sectarian balance.
Syria's ambassador to Lebanon, Ali Abdul Karim Ali, said his country understood the new rules, but urged "coordination" with Damascus, in a statement quoted by Lebanon's National News Agency.
The new rules raise the prospect of Syrians being unable to flee the violence that has killed more than 200,000 people since March 2011.