UNITED NATIONS: Russia on Thursday blocked adoption of a draft U.N. statement condemning a deadly Syrian mortar attack on a Turkish town and proposed a weaker text calling for "restraint" on the border without referring to breaches of international law.

Western diplomats complained that Russia's proposed Security Council statement, if accepted, would weaken the message to an unacceptable degree.

U.N. Secretary-General Ban Ki-moon was "alarmed by escalating tensions along the Syrian-Turkish border" and worried that the risk of a wider regional conflict was growing, U.N. spokesman Martin Nesirky said.

Syria, meanwhile, wrote to the Security Council calling for restraint.

"The members of the Security Council called on the parties to exercise restraint and avoid military clashes which could lead to a further escalation of the situation in the border area between Syria and Turkey," said Russia's proposed statement, obtained by Reuters.

If adopted, the non-binding statement would also call on the two neighbors to "reduce tensions and forge a path toward a peaceful resolution of the Syrian crisis."

The Syrian mortar attack on Wednesday killed five Turkish civilians.

Some 30,000 people have been killed across Syria in the 18-month-long conflict between forces loyal to President Bashar al-Assad and rebels seeking to oust him, opposition activists say. The civil war is seeing growing sectarian overtones which threaten to draw in regional Sunni Muslim and Shi'ite powers.

The Russian draft keeps some of the language in the original text proposed by Azerbaijan, and urges the Syrian government to investigate the attack.

The original draft, circulated to the 15-nation council on Wednesday, condemned "in the strongest terms" the Syrian army's shelling of a town in Turkey and demanded an end to violations of Turkish territory. Both drafts say the border tensions were an "alarming" spillover of the conflict outside Syria.

However, the Russians proposed removing the following sentence, which diplomats said was crucial: "Such violations of international law constitute a serious threat to international peace and security."

U.N. envoys say that was to signal that the Security Council, which is supposed to guard international peace and security, should remain involved in the matter.

Another problem with the Russian proposal, Western diplomats said on condition of anonymity, is that it attempts to balance the Syrian attack with the Turkish response. It shifts the blame from the Syrian army, they said, by suggesting an investigation is needed on whether the Syrian army was behind the attack.

Council envoys said they would continue negotiating on a text. U.S. Ambassador to the United Nations Susan Rice told reporters the council needs to "clearly and unequivocally" condemn the attack and urge an end to such action.

Rice said the attack on Turkey was "very destabilizing and must be stopped." She added that a number of council members found the Russian proposal unacceptable.

Security Council statements must be agreed to unanimously.

The decision to try to issue a council statement was a response to a request from Turkey, which asked council members on Wednesday to take the "necessary action" to stop Syrian aggression and ensure that the government there respect Turkish territorial integrity.

"This is an act of aggression by Syria against Turkey," Turkish U.N. Ambassador Ertugrul Apakan said in a letter to the president of the 15-nation Security Council, Guatemalan Ambassador Gert Rosenthal.

"It constitutes a flagrant violation of international law as well as a breach of international peace and security," said the letter, obtained by Reuters.

Syria also wrote to the council offering condolences for the deaths of Turkish civilians, calling for restraint and rationality, and reiterating that Syria respects the sovereignty of its neighbors. It also offered details of Turkey's response.

"Turkish forces fired artillery shells towards Syrian territory on the southern side of Tal Abyad village," the letter said. "It stopped at midnight and then at 7 a.m. on Thursday it resumed the shelling.

"Two officers were wounded because of the shelling and our forces exercised self-restraint and did not respond to the Turkish shelling," it said.

It is unlikely that the council would do more than issue a statement for the time being, though getting agreement on a text may not be easy. The council has been deadlocked on Syria's conflict for more than a year.

Russia, a staunch ally of Syria, and China have vetoed three resolutions condemning Assad's government. They also reject the idea of sanctioning those in power in Syria who are responsible for the military assault against the opposition.