(CNN) -- Bloody clashes erupted Saturday between pro- and anti-Syrian regime fighters in the Lebanese city of Tripoli, the deadliest outburst of violence in recent weeks and further indication that Syria's turmoil is spilling across borders.
Twelve people were killed and approximately 50 were wounded in the latest fighting, according to the state-run National News Agency. Of those hurt, 12 were transported to a hospital in the coastal city, including one in critical condition.
At one point, a continuous stream of "rocket bombs" hindered national security forces' attempts to secure the area, the news agency said. One rocket exploded over a well-known castle in the city, while another landed some distance away.
Prime Minister Najib Mikati went to Tripoli to assess the security situation, state news reported.
After meeting with leaders from the different factions involved in the clashes, Interior Minister Marwan Charbel announced that national security forces will enter the area to enforce a cease-fire set to begin at 5 a.m. Sunday.
Anyone who does not abide by the cease-fire "will bear responsibility," said Charbel, according to the official news agency.
The sectarian violence in Tripoli -- which is on the Mediterranean coast, about 50 miles from Homs in Syria -- mirrors the tensions in its neighboring nation.
Clashes in both nations pit Sunnis, who make up the majority of the Syrian opposition and population, against Alawites and other Shiites, who are dominant in President Bashar al-Assad's government.
Sunnis are the majority in northern Lebanon, where Tripoli is located and where anti-Assad factions are relatively strong. The Syrian president, meanwhile, has more support in southern Lebanon and among members of the powerful Shiite militant and political group Hezbollah, which is considered a terrorist organization by U.S. authorities.
Saturday's fighting is not the first time tensions have simmered over, including in Tripoli.
Last month, violence flared after Lebanese authorities arrested Chadi Mawlawi, an Islamist activist who was helping Syrian refugees by providing food and shelter, his cousin said. Lebanon had accused Mawlawi of being an operative in an al Qaeda-inspired group -- something his relatives deny.
The activist was eventually released, but not before his arrest sparked fighting that killed seven people and left dozens wounded.
Elsewhere in Lebanon, the kidnapping of a group of Shiite Muslim pilgrims in Syria prompted angry protests last month in Beirut, the capital.
Also last month, gun battles in Beirut between rival political parties -- one supporting Syria's al-Assad and one opposing him -- left two dead and 18 wounded. That was the worst outbreak of violence in a city where the powerful Hezbollah militia engaged government troops in street battles in 2008.
That bloodshed came hours after Lebanese troops killed two Sunni Muslim clerics -- both opposed to the embattled Syrian regime -- at a checkpoint in northern Lebanon.
Syria has long been a major influence in Lebanon, and not just because of the extensive border the two nations share.
Lebanon was considered part of "greater Syria" until the end of World War I. Syrian troops were deployed in Lebanon between 1976 and 2005, primarily in the north -- ostensibly at first as peacekeepers to help stop Lebanon's long civil war, though they stayed long after the fighting stopped in 1990.
The Syrian forces' 2005 withdrawal followed the car-bomb killing of former Prime Minister Rafik Hariri in Beirut, which some blamed on elements of al-Assad's regime. Since then, Lebanon's most prominent political blocs have been sharply divided -- the ruling pro-Syria alliance led by Prime Minister Najib Mikati on one side and anti-Syrian factions led by Saad Hariri, the son of the assassinated former prime minister, on the other.
The unrest in Syria that began 15 months ago with peaceful anti-government protests, followed by a government crackdown, has meant further complications for Lebanon.
Thousands of refugees have poured across the border. And in April the Lebanese army announced it had intercepted a cargo ship bound for Tripoli that was filled with weapons it believes were meant to be delivered to rebel forces in Syria.
CNN's Hamdi Alkhshali and Nick Thompson contributed to this report.