It was also a suspension of construction projects involving Turkish firms. Russia was the biggest source of Turkish imports. The Russian Su-24, an all-weather attack aircraft, was shot down by Turkish F-16s in the Turkey-Syria border area on 24 November. The Russian defence ministry insisted that the aircraft remained within Syria’s borders throughout its mission and did not violate Turkish airspace and received no warnings. Mr Putin said at the time the restrictions would not be lifted until Russia received an apology. Even Mr Erdogan offered to meet Mr Putin in person Moscow refused. By sending the letter, Turkish President Recep Tayyip Erdogan asked in fact to a normalization of relations between the two countries.