At least 10 people have been killed and 30 wounded in northern Lebanon amid fears that the continuing crisis in Syria could spill over into all-out sectarian war in the region.

The gun battle in the town of Tripoli is the worst non-Syrian outbreak of violence inspired by the conflict so far and came as the international peace envoy Kofi Annan warned of an "alarming sectarian dimension" to the conflict.

The violence broke out late on Friday between residents of the mainly Sunni Bab Tabbaneh neighbourhood and the adjacent Alawite-majority Jabal Mohsen, and continued on Saturday.

"We are being targeted because we support the Syrian people," a Sunni gunman told AP. "We are with you [the Syrian people] and will not abandon you." Residents have been fighting for weeks but the violence had not reached the intensity of this weekend.

In Qatar's capital, Doha, Annan urged the Syrian president, Bashar al-Assad, and his opponents to immediately implement his peace plan. "The spectre of an all-out war, with an alarming sectarian dimension, grows by the day," he told a meeting of members of the Arab League, co-sponsor with the United Nations of the peace plan aimed at ending violence in Syria.

Meanwhile, skirmishes in Syria continued on Saturday, according to monitoring groups. The Syrian Observatory for Human Rights said the recent death toll included 14 soldiers: six in Dera'a and eight in confrontations with the Free Syrian Army, which did not report any casualties.

The London-based Syrian Observatory also reported the killing of 54 people, including 17 soldiers, on Friday. None of the reports could be independently verified.

The violence continues to drive people from their homes and cause international tension. Turkish officials reported that 400 Syrian refugees had arrived in Turkey from Syria's Idlib province. There are now 24,500 Syrian refugees in Turkey and around 73,000 in all neighbouring countries.

A French poll on Saturday showed a strengthening of support for a military intervention in Syria. The Ifop poll – the first since last week's mass killings in the town of Houla – revealed 58% now backed a military intervention, up from 51% in February, and support for French involvement had surged to 50% from 38%.

Ifop said the increase was "undoubtedly linked to the multiplication of war crimes blamed on Bashar al-Assad's regime and their recent media coverage".

Outrage at the Houla killings prompted France to join several western nations in stepping up pressure on Syria by expelling senior diplomats and calling on Russia to allow tougher action by the UN security council.

France's new president, François Hollande, said on Tuesday that military intervention could not be ruled out as long as it was carried out under the auspices of a UN security council resolution.

The UN commissioner for human rights has warned Assad and his supporters that there can be no amnesty for crimes committed under their regime. Navi Pillay said peace negotiators seeking to offer amnesties in return for regime change would be acting beyond their powers.

"You cannot have amnesty for very serious crimes," she told AP, "so my message is very clear – there has to be accountability."