New restrictions on Syrians entering Lebanon have come into effect, further slowing the flow of people trying to escape the war.
Previously, travel between the two countries was largely unrestricted, but now Syrians will have to obtain a visa.
Lebanon hosts more than a million Syrian refugees and this is the latest step to try to stem the influx.
Millions of Syrians have been displaced by the civil war as rebel forces try to oust President Bashar al-Assad.
The uprising began with protests against his rule in 2011 and degenerated into civil war a year later. The rise of Islamist groups has added to the refugee problem.
Lebanon, which shares a border with Syria, is one of the countries most affected by the large numbers of refugees.
Before now, Syrians could stay in Lebanon for up to six months automatically. Under the new measure, Syrians wanting to enter Lebanon will have to fulfil certain criteria in order to be granted a visa at the border.
It is unclear what the rule will mean for the many Syrians already in the country and not registered as refugees.
At the scene: Paul Wood, BBC News, Mashha, northern Lebanon
The small town of Mashha has 6,500 residents. Now, 3,500 refugees have made it their home too. As elsewhere in Lebanon, rents are rising, wages are falling and Lebanese complain they can't find jobs.
"I used to earn $1,000 a month," one resident told me. "They sacked me, and hired four Syrians instead."
Those resentments boiled over a few weeks ago, when an angry mob burned down a new camp built by an international charity.
And Mashha is Sunni, like the bulk of the refugees. Elsewhere in Shia and Christian areas the influx is widening sectarian and religious divisions.
Behind the economic hardships lie the fears many Lebanese have, that the presence of more than a million refugees in the small fragile country might eventually trigger a renewed civil war.
Every Syrian wanting to enter the country will need to state a clear purpose for their visit, and, if approved, a visa will be issued for a certain duration.
Syrians coming to work in Lebanon will also have to be sponsored by a Lebanese individual or company.
A spokesman for the UN refugee agency (UNHCR) in Lebanon, Ron Redmond, said that over the past six to eight months several measures had already reduced the number of people seeking registration as refugees. But the UN had worked out a system with the government to enable the most vulnerable to still gain access.
Mr Redmond told BBC Newsday he wanted the government to clarify that the most vulnerable could still get through.
"The government says that it will allow those extreme humanitarian cases access but it is not covered in these announcements that have come out the last few days," he said.
Khalil Jebara, an adviser to Lebanon's interior minister, told the BBC that Lebanon "will only allow refugees under very limited and exceptional cases."
Permits for refugees would need to be signed by Lebanon's social affairs ministry, as well as its interior ministry, he added.
Lebanon has long been struggling to cope with the number of refugees fleeing the war in Syria.
There are currently more than 1.1 million registered refugees in Lebanon putting a huge strain on the country's infrastructure and resources.
The Lebanese government says the actual number of refugees in the country is about 1.6 million.
Clearly the Lebanese government wants to reduce the flow, says Rami Khouri, Senior Fellow at the Issam Fares Institute at the American University of Beirut.
"The Lebanese are trying to figure out how to really remain helpful to Syrians in real need without destroying their own country," he told the BBC.
Many refugees live in poor conditions.
"Life in Syria was better than it is here, and if I had the money to return I would," Mohammed, an elderly man who brought his family from Yarmouk in southern Damascus, told the BBC for a report in April on the plight of Syrian refugees in Lebanon.
In October, Lebanon's social affairs minister announced that the country would stop accepting all refugees except emergency cases, but would still allow Syrians to enter for other purposes, such as work and tourism.
The latest UNHCR figures show a total of 3.2m Syrians registered as refugees in Lebanon and elsewhere.
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