By Ed Cropley
BEIRUT, April 28 (Reuters) - Gunmen in inflatable dinghies killed several security officials in an attack on a military unit on Syria's Mediterranean coast, state media said on Saturday, the first seaborne assault reported during the revolt against President Bashar al-Assad.
The night raid, along with the killings of at least 15 people in violence in two areas near the capital, underlined the threadbare state of a U.N.-brokered ceasefire deal that has Western leaders talking of tougher steps to stop the bloodshed.
Russia, Damascus' most powerful ally, stepped up its criticism of anti-Assad militias, condemning what it called "barbarous" attacks designed to scuttle the two-week-old truce engineered by U.N.-Arab League mediator Kofi Annan.
Syria's official SANA news agency said several gunmen and soldiers died in fighting that followed the coastal attack near the northern port of Latakia, 35 km (22 miles) south of the Turkish border.
"The fighting ... resulted in the death and wounding of a number of military personnel while the number of those killed from the terrorist group was not known because they attacked the military unit at night," SANA said.
It did not state the nationality of the attackers.
Damascus has accused Turkey of allowing weapons and funds to flow to insurgents throughout the 13-month-old uprising, the latest in a wave of revolts against rulers across the Arab world. Turkey also plays host to the leadership of the rebel Free Syrian Army.
Lebanese authorities found weapons including rocket-propelled grenades and rifles on board a ship intercepted in the Mediterranean which may have been trying to supply Syrian insurgents, security sources said.
In a village north of Damascus where army defectors had taken refuge, activists said Syrian forces killed at least 10 people. And overnight, five members of the security forces were killed in an explosion targeting two vehicles near Damascus, the UK-based Syrian Observatory for Human Rights said.
The United Nations says Syrian forces have killed 9,000 people since the start of the revolt in March 2011. Syrian authorities blame foreign-backed militants for the violence and say 2,600 soldiers and police have been killed.
Annan's April 12 ceasefire has led to only modest reductions in the level of daily carnage, with both sides accusing each other of multiple breaches of the truce.
On Friday, a suicide bomber killed nine people when he detonated an explosives belt outside a Damascus mosque.
SANA said six officials killed in that blast were buried on Saturday, along with a further 16 army and security personnel killed in separate incidents elsewhere in the country of 23 million.
Most independent media have been barred from Syria, making it hard to verify accounts of events on the ground. SANA named all the people it said were buried on Saturday.
The Damascus suicide attack was just one of five explosions to hit the capital on Friday, creating the impression insurgents may be changing tactics and embarking on a sustained bombing campaign aimed at the seat of Assad's power.
"The action is picking up and it seems the (rebels) and Assad's forces are starting to battle it out in Damascus as well," said one activist based in the capital who uses the name Mar Ram.
U.N. Secretary-General Ban Ki-moon has accused Damascus of breaking its pledge to withdraw heavy weapons and troops from towns, and said he is "gravely alarmed by reports of continued violence and killing in Syria".
Syrian media hit back, say Ban was inflaming the conflict by ignoring "crimes and terrorist actions" committed by anti-Assad militiamen.
"His focus on shamefully pointing at Syria, as usual, encourages these groups to continue to commit more crimes and terrorist acts," the state newspaper Tishreen said.
Russia also piled in, saying the disparate rebel groups trying to topple Assad appeared determined to trash what is left of the U.N.-backed peace initiative.
"Attempts by the irreconcilable opposition to increase tension even more and incite violence cause particular alarm," Moscow said in a statement. "The aim is clear: to ruin a solution in Syria based on Annan's plan."
U.N. monitors are trickling in and officials say 30 of a planned 300-strong mission should be in place by Monday to reinforce observers already stationed in anti-Assad hotbeds such as Idlib, Hama, Homs and Deraa.
The slow build-up, more than two weeks after the truce came into effect, has been derided by Assad's foes and intensified frustration in Western capitals, where leaders want firmer measures imposed on Damascus sooner rather than later.
The presence of the monitors has emboldened many thousands of protesters to resume demonstrations after weeks of military crackdown, but activists say Assad's forces responded swiftly.
Security forces carried out house to house raids in the Damascus suburb of Irbin on Saturday, arresting demonstration leaders who welcomed the observers a week ago, two resident activists said.
France says that if Assad's forces do not return to barracks, it will push next month for a "Chapter 7" U.N. Security Council resolution - which could allow action ranging from economic sanctions to military intervention.
Russia and China have made clear that they would veto Libya-style military action and have resisted the idea of sanctions. (Additional reporting by Khaled Yacoub Oweis and Dominic Evans; Editing by Andrew Heavens)