UNITED NATIONS, Oct 4 (Reuters) - U.N. Secretary-General Ban Ki-moon was "alarmed by escalating tensions" between Syria and Turkey and warned that the risk of the 18-month-long Syrian conflict embroiling the entire region was growing, his spokesman said on Thursday.

"The Secretary-General is alarmed by escalating tensions along the Syrian-Turkish border," Ban's spokesman Martin Nesirky told reporters. "As the situation inside Syria deteriorates yet further ... the risks of regional conflict and the threat to international peace and security are also increasing."

A mortar bomb from Syria landed in Turkey on Wednesday, killing at least five people. Turkey responded later the same day by striking targets in Syria. Turkey asked the U.N. Security Council to take the "necessary action" to stop Syrian aggression and ensure Turkish territorial integrity is respected.

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  • Turks hold banners that read "no to war" during a protest in Istanbul, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • Turks hold banners that read " no to imperialist intervention in Syria " during a protest against a possible war with Syria, in Istanbul, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • Turks hold cartoons depicting Turkey's Prime Minister Recep Tayyip Erdogan as they protest against a possible war with Syria, in Istanbul, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • Turks hold banners that read " we will take you down from your throne" during a protest against a possible war with Syria, in Istanbul, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • Turks hold banners that read " we will not bow heads" during a protest against a possible war with Syria, in Istanbul, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • Turks hold banners that read "no to war, no to fascism" during a protest in Istanbul, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • Turkish military stand near the Turkey-Syria border in Akcakale, Turkey, early Friday, Oct. 5, 2012. (AP Photo)

  • Turks hold banners that read" No to War" during a debate at Turkey's parliament in Ankara, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • Riot police use pepper gas against the Turks protesting against a possible war with Syria during a debate at Turkey's parliament in Ankara, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • Turks hold banners that read" No to War" during a debate at Turkey's parliament in Ankara, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • In this Monday, Oct. 1, 2012, photo, Prime Minister Recep Tayyip Erdogan, center, and his deputies Bulent Arinc, right, and Besir Atalay seen at Turkey's parliament in Ankara, Turkey. (AP Photo)

  • The lawmakers seen during a debate at Turkey's parliament in Ankara, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • The ruling party lawmakers and ministers, rear, seen during a debate at Turkey's parliament in Ankara, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • Deputy Turkish Prime Minister Ali Babacan, left, Foreign Minister Ahmet Davutoglu, second right, and other ministers listen during a debate at Turkey's parliament in Ankara, Turkey, Thursday, Oct. 4, 2012. (AP Photo)

  • In this image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, smoke rises from houses due to government shelling in Damascus, Syria, on Thursday, Oct. 4, 2012. (AP Photo/Shaam News Network via AP video)

  • In this image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, smoke rises from houses due to government shelling in Damascus, Syria, on Thursday, Oct. 4, 2012. (AP Photo/Shaam News Network via AP video)