ISTANBUL/OSLO: A United States warship crossed Turkey's Bosphorus Strait on Friday, headed towards the Black Sea, as tensions simmer over Ukraine's Crimea region.

A coastguard boat was seen escorting the guided-missile destroyer, the USS Truxtun.

The US Navy said in a statement on Thursday that the ship was bound for the Black Sea to conduct military exercises with Bulgarian and Romanian naval forces.

According to the Montreux Convention, warships of countries which do not border the Black Sea can only stay in the waters for 21 days.

On Tuesday, two Russian warships crossed the Bosphorus after the Kremlin “summoned” the vessels back to its Black Sea fleet to strengthen its military presence in Crimea.

A Ukrainian vessel also entered the Black Sea the same day, according to the Turkish state-run Anatolia news agency.

The increased sea traffic comes at a time of growing tension between the West and Russia over Crimea, a predominantly ethnic Russian peninsula housing the Kremlin's Black Sea fleet.

Nato holds ‘invasion’ exercise in Norway

Nato is launching a military exercise involving 16,000 soldiers from 16 countries in the north of Norway, to practise stopping a surprise invasion, the Norwegian army announced on Friday.

The army was quick to add that the multi-national exercise dubbed Cold Response had been planned for a long time and had nothing to do with the current tensions between the West and Russia over Ukraine, where Russian forces have taken effective control of Crimea.

“We have been working on this scenario for two years,” Lieutenant Colonel Terje Bruoeygard, a spokesman for the exercise, said.

According to the Norwegian officer, the exercise involving air, sea and land forces will simulate a surprise invasion of the country by a fictitious nation from the north followed by an intervention by allied forces.

The goal is to train troops of the Nato alliance in combat in a cold environment like northern Norway near the Arctic Circle. There will be international observers including Russians.

It involves 9,000 Norwegian soldiers and 7,000 from other Nato countries, including Britain, France and the United States, as well the non-aligned Sweden and Switzerland.

This year will mark the seventh time Nato has held this military exercise since 2006, with the major manoeuvres taking place between March 12-19.—AFP