* Cargo ship carrying ammunition, Cypriot official says
* Russia is one of Syria's last remaining allies
* Ship had docked in Cyprus to refuel during storm (Adds U.S. concerns)
MOSCOW/NICOSIA, Jan 13 (Reuters) - A Russian-operated ship carrying a cargo of ammunition has reached conflict-torn Syria after being temporarily halted during a refuelling stop in Cyprus, sources in Russia and Cyprus said on Friday.
A source in Cyprus, where the ship made a stop for refuelling on Tuesday, said the ship had given written assurances its destination would not be Syria but Turkey.
It was allowed to sail a day later, whereupon it dropped off conventional tracking systems, switched course and reached Syria on Thursday.
"It had bullets. There were four containers on board," a Cypriot official told Reuters.
Russia has long been a major arms supplier to Syria, where President Bashar al-Assad has been trying to crush a 10-month-old wave of unrest, raising an international outcry and triggering Western and Arab sanctions against Damascus that Moscow has refused to join.
In Russia, a source at the vessel's St. Petersburg-based firm said the ship Chariot had reached Syria, but declined to comment on reports the ship was carrying cargo from Russia's state weapons exporter Rosoboronexport.
The Chariot sailed from St. Petersburg on Dec. 9.
"The ship was carrying a dangerous cargo," the source at St. Petersburg-based Westberg Ltd. said by telephone on condition of anonymity. "It reached Syria on Jan. 11th."
Rosoboronexport spokesman Vyacheslav Davidenko said the arms exporter would neither confirm nor deny the report. "We do not comment on where our deliveries go, when they leave port or how."
A Turkish foreign ministry official on Friday confirmed the ship had reached Syria.
"As of 10:15 a.m. (0815 GMT) yesterday the Turkish navy checked and confirmed that the ship in question was docked at the Syrian port of Tartus," ministry spokesman Selcuk Unal said.
Russia has voiced strong opposition to arms embargoes and has promised to uphold arms contracts with Syria, one of its top weapons customers, despite increasing international pressure.
Cyprus, an EU member with traditionally close ties to Russia, has maintained it was obliged to allow the vessel to go.
"Since it had changed destination, and (if) we would not have allowed it to go, the company could cite illegal detention of a ship," the Cypriot official said.
The island has bitter experience in dealing with confiscated arms destined from one sanction-hit country to another.
Last July, confiscated munitions destined for Syria from Iran exploded, destroying Cyprus's largest power station in its worst peace-time disaster and pushing it to the brink of seeking an EU bailout. Locked out of international capital markets, it recently clinched a 2.5 billion euro ($3.2 bln)loan from Russia.
In November, Russian Foreign Minister Sergei Lavrov called full weapons embargoes against Syria "dishonest", suggesting that in practice they cut off military supplies to the government while allowing opposition forces to attain arms from abroad at will.
An unnamed military source was quoted as saying in December that Russia had delivered anti-ship Yakhont missiles to Syria.
Syria accounted for 7 percent of Russia's total of $10 billion in arms deliveries abroad in 2010, according to the Russian defence think tank CAST.
RUSSIA'S NAVAL BASE
The European Union said it was aware of the case and national authorities were responsible for making sure an EU arms embargo is upheld.
"We are instrumental in putting these measures in place but it's up to the national authorities to make sure they are implemented and as far as I'm aware the authorities in this case are confident that the embargo has not been broken," said Michael Mann, spokesman for Catherine Ashton, the EU's high representative for foreign affairs.
The United States said it had raised concerns with Moscow over the ship.
With regard to the ship we have raised our concerns about this both with Russia and with Cyprus, which was the last port of call for the ship, and we are continuing to seek clarification as to what went down here," State Department spokeswoman Victoria Nuland said.
The Westberg official said the company had done nothing wrong as no Russian law prevented the delivery from being made at Syria's Tartus port, where Russia maintains a naval base.
"The ship went to Syria as there was nothing illegal in reaching its originally intended destination," he said.
In October, Russia and China vetoed a western European-led resolution on Syria that threatened sanctions for the bloodshed the U.N. says has killed 5,000 people, Russia tabled a new draft resolution last month.
The move briefly raised Western hopes of Security Council action, but Western diplomats have complained that Moscow has not seemed enthusiastic about pursuing negotiations on the text, raising suggestions Russia may be helping Assad play for time.
A senior Russian diplomat blamed Western nations in the Security Council for the lack of progress on the draft, saying they had suggested changes Moscow disagreed with.
"Unfortunately the Western approach differs from ours and judging by the contents of the amendments which were presented, factually put forth a goal of regime change of B. Assad in Damascus," Deputy Foreign Minister Gennady Gatilov said.
He said, however, Russia was "ready for dialogue ... with the aim of coming to a mutually acceptable text" and consultations would take place this week.
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($1 = 0.7895 euros) (Additional reporting by Michele Kambas in Nicosia, Luke Baker in Brussels and Simon Cameron-Moore in Istanbul; Editing by Sophie Hares)