* Ten civilians die in bus attack; soldiers die in ambushes
* Army turns heavy guns on Hama, Sermeen -activists
* U.N. Security Council statement has little impact
By Oliver Holmes and Crispian Balmer
BEIRUT, March 22 (Reuters) - More than 40 people died in clashes across Syria on Thursday, opposition activists said, as a U.N. Security Council call for an immediate end to the fighting fell on deaf ears.
In the worst incident 10 civilians, including three children and two women, died when their small bus was shot up in the northern town of Sermeen as they tried to flee to Turkey, the British-based Syrian Observatory for Human Rights (SOHR) said.
The SOHR, which depends on a network of local contacts for its information, said it was not clear who was behind the killings. Other activists blamed the Syrian army, which has been trying to stamp out insurgents in the area.
Dozens of civilians were killed in other parts of the northern province of Idlib, in Homs, Hama and Deraa in the south of the country, it said. Five rebel gunmen and seven soldiers were killed in clashes in Homs province, it added.
U.N. Secretary General Ban Ki-moon said Wednesday's unanimous Council statement had sent a clear message to Syria to end all violence, but Damascus appeared to dismiss the document, which is not legally binding.
At least 8,000 people have died in the year-long revolt against President Bashar al-Assad, according to U.N. figures issued a week ago, with a motley assortment of fighters grouped in the rebel Syrian Free Army taking on the security apparatus.
Syrian Foreign Ministry spokesman Jihad Makdesi said this week that 3,000 members of the security forces had died in the uprising, which Damascus blames on terrorist gangs.
Heavily armed government forces have made advances in recent weeks, sweeping armed opponents from strongholds around Syria, but they appear to be struggling to consolidate their gains.
Opposition sources said tanks had once again shelled a neighbourhood in the northeastern city of Hama, which has been a centre of revolt. Opposition sources said at least 20 people had died in army attacks there in the last 48 hours.
It is impossible to verify reports from Syria because authorities have denied access to independent journalists.
Syrian troops also turned heavy guns on Sermeen.
"Syrian forces are still not able to get inside the town because of fighting, but they are shelling Sermeen and using heavy machineguns," said SOHR head Rami Abdelrahman.
In addition, the SOHR reported heavy fighting in al-Qusair, a town close to the Lebanese border. Three residents died in the fighting and four soldiers were killed in an ambush.
Fighting also erupted in southern Deraa, he said, and Assad's forces conducted raids in the eastern province of Deir al-Zor and coastal Latakia province to try to snuff out the rebellion.
The Security Council's statement was supported by Russia and China, which had both vetoed previous Council resolutions, marking a rare moment of global unity over the crisis.
It backed a peace drive by U.N.-Arab League envoy Kofi Annan, calling for a ceasefire, political dialogue and full access for aid agencies. It also says the army should stop using heavy weapons in populated areas and pull troops back.
Turkish Foreign Minister Ahmet Davutoglu said world powers needed to work together much harder to end the bloodshed, saying the Council statement was just "a common message".
"We also need to work out a common action plan," he told reporters during a visit to Vienna on Thursday.
The U.N. statement talks of the need for political transition in Syria but does not demand that Assad step down - something both the rebels and the Arab League have called for.
Syria's official news agency appeared to shrug off the document, saying it contained "no warnings or signals".
Diplomats say that without swift resolution, the conflict risks spilling over into neighbouring countries and heightening already tense sectarian ties, with the uprising setting Assad's minority Alawite sect against a Sunni Muslim majority.
Underlining the dangers, several stray Syrian shells fell in the Lebanese border village of al-Qaa and nearby fields late on Wednesday, wounding one person, residents said. Gunfire could be heard in the border area again on Thursday.
Human Rights Watch accused Syrian forces of using the same "brutal methods" in Qusair as it had during the siege of Homs.
"Having seen the devastation inflicted on Homs, the Russian government should stop arms sales to the Syrian government or risk becoming further implicated in human rights violations," said Sarah Leah Whitson, the group's Middle East director.
Russia has defended its long-standing military ties with Syria and has said it sees no reason to modify them.
The European Union is set to impose further sanctions on Assad's inner circle on Friday, including his wife Asma, who described herself as "the real dictator" in an email published by Britain's Guardian newspaper last week.
"Tomorrow we will decide on new sanctions, not only against the Assad regime but also against the people around him," German Foreign Minister Guido Westerwelle told Deutschlandfunk radio.
Referring to Moscow's support for the U.N. statement, he said: "Assad cannot depend on the protective hand of Russia in the violence against his own people and that could accelerate the process of erosion of the regime."
Although Russia has stuck to its demand that Assad must not be deposed by foreign powers, it has taken a sterner line this week, accusing the Syrian leadership of mishandling the crisis.
Analysts say this shows Russia is hedging its bets about Assad's fate and is positioning itself for his possible fall.
"Russia will not be focused on keeping Assad in power for the sake of keeping Assad in power," said Dmitry Trenin, director of the Carnegie Moscow Centre think tank.
Envoy Kofi Annan plans to go to Russia soon for talks on Syria, his spokesman said in Geneva on Thursday, but declined to be more specific.
British Foreign Secretary William Hague said international pressure on Syria would rise until there was a ceasefire.
"As long as this killing goes on we have to increase the pressure as well as consider what steps to take in the U.N. Security Council," he told a news conference in Rome.
Hague welcomed Chinese and Russian support for the U.N. statement, but added: "This does not mean it is immediately possible to agree on a Security Council resolution."