Syria has warned it may strike at rebels hiding in neighbouring Lebanon if the Lebanese army does not act, as its patience "is not unlimited", the state news agency SANA has said.
Syria's Foreign Ministry told its Lebanese counterpart yesterday that a "large number" of militants had crossed Lebanon's northern border into the Syrian town of Tel Kalakh over the past two days, SANA said.
"Syria expects the Lebanese side to prevent these armed terrorist groups from using the borders as a crossing point, because they target Syrian people and are violating Syrian sovereignty," the diplomatic cable said.
It said Syria's "patience is not unlimited", even though "Syrian forces have so far exercised restraint from striking at armed gangs inside Lebanese territory".
Fighting near the border resulted in a large number of casualties, SANA said, before the gunmen retreated into Lebanon.
Lebanon has a policy of "dissociation" from the two-year-old civil war in Syria.
However, officials say they feel their country is increasingly at risk of being dragged into a conflict that the United Nations says has killed 70,000 Syrians.
More than 1m Syrians are believed to have taken shelter in Lebanon.
They live among a nation of 4m, which fought its own devastating 1975-1990 civil war and whose own sectarian tension between Christians, Sunni and Shia Muslims have been heightened by the fighting in Syria.
Tension between Lebanese groups that support the Syrian opposition and those that support Syrian President Bashar al-Assad have been intensifying and have sometimes turned violent.
The final day of an EU summit focused on the Syrian conflict, with Britain and France pushing for an end to the arms embargo that stops them from arming rebels in the country.
European Council President Herman Van Rompuy said there was a growing frustration among EU leaders that the bloody conflict in Syria is continuing.
He said that they had tasked their foreign ministers to discuss the question of the arms embargo, and find a common position.
EU foreign policy chief Cathy Ashton and German Chancellor Angela Merkel both raised concerns about lifting the arms embargo against Syria.
There were no signs as the summit ended of any majority in favour of an early change in the sanctions regime as requested by the UK and France.
Baroness Ashton warned that lifting the arms blockade could be seized on by supporters of the regime to channel even more arms to bolster Assad's military campaign.
Chancellor Merkel told journalists she was ready to talk on the issue, but was still considering Germany's position.
French President Francois Hollande said: "We are fighting terrorism around the world.
"We have been helping the opposition in Syria and want to go further.
"We trust the opposition - we do not want Syria to become another Libya."
Meanwhile, the International Committee of the Red Cross has appealed to foreign powers to press combatants in Syria to halt attacks on civilians and aid workers, saying all sides were violating the Geneva Conventions.