U.S. Air Force Lt. Col. Lendy Renegar, commander of the 48th Air Expeditionary Group out of RAF Lakenheath, England, hands over the ceremonial key to the Polish and British commanders as they take over responsibility for patrolling the Baltic airspace at Siauliai air base in Lithuania on Wednesday, April 30, 2014.

RAF MILDENHALL, England Three NATO nations assumed control on Thursday of a strengthened Baltic air policing mission from the U.S. Air Force amid the worsening crisis in neighboring Ukraine.

Separately, Canada is sending six interceptors to Romania as a sign of allied solidarity with its east European members bordering Ukraine and Russia.

Poland, Britain and Denmark are providing a total of 12 fighters to replace 10 F-15C Eagles from RAF Lakenheath, England, according to a NATO statement. The three nations are scheduled to operate the mission for four months.

Additionally, the French deployed four jets to Poland to replace the MiG-29s Poland sent to the Baltics, a NATO official said.

The Baltic mission normally consists of four fighters provided by a single NATO nation to serve as a rapid-reaction force to intercept unidentified or suspicious planes in or near Baltic airspace. The three Baltic nations Estonia, Latvia and Lithuania dont possess fighter jets capable of patrolling their own airspace.

Weve tripled the air presence, roughly, in the region and the purpose is to show an air presence, to demonstrate commitment to NATO solidarity and to be able to respond appropriately to any inappropriate activity by other parties, Gen. Adrian Bradshaw, NATOs deputy supreme commander, said in a press release.

Poland and the United Kingdom will fly out of Siauliai air base, Lithuania, the traditional base of the mission since its inception in 2004. Danish planes will fly out of Amari air base, Estonia, which Lakenheaths airmen recently helped certify for NATO use. The French jets will operate from the Malbork airbase in Poland, the NATO statement said.

Lakenheath initially deployed four F-15Cs and about 150 airmen for the mission in early January, but the Baltics requested additional security as Russia was moving to annex Crimea from Ukraine at the time.

The change of responsibility comes just days after NATO planes scrambled to intercept a Russian aircraft, a NATO official said in a telephone interview. The aircraft was flying over international waters on Monday, but had not filed a flight plan or used a transponder detectable by civilian air traffic control.

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NATO allies take over Baltic mission from Air Force