"We are not closing the door to the Patriot, it all depends on the price, the possibility of technology transfer, joint production and other four or five important points… We have received the best offers from Russia. If the United States provides us with good conditions, we will also evaluate them," Kalin said at a briefing in Ankara.
The spokesman underlined that the possible Patriot purchase was not an alternative to S-400.
"The deliveries of the [Russian-made] S-400 systems will not be affected, and they will begin in 2019. This is not an alternative, but two parallel processes," the spokesman stressed.
The statement followed last week's announcement by the Pentagon, saying that the US State Department had approved a possible $3.5 billion sale of Patriot systems to NATO-ally Turkey.
The Patriot sale comes in line with Washington's attempts to thwart the Russian S-400 air defence systems' sale to Turkey ever since the contract was signed on December 20. Previously, the US was threatening to halt F-35 jet shipments to Ankara.
Reacting to this report, Kremlin spokesman Dmitry Peskov said that the Russian-Turkish contract envisages Ankara's non-disclosure of certain data.
S-400 Triumph (NATO reporting name SA-21 Growler) is Russia's most advanced surface-to-air missile system. It has a range of 400 kilometres (248 miles) and is capable of tracking and destroying all existing aerial targets, including ballistic and cruise missiles.
Turkey to Coordinate With Russia Its Actions East of Euphrates
The Turkish presidential spokesman has also spoken about the country's action in Syria.
"We will also work closely with Russia on the issue of coordination of actions east of the Euphrates, in addition to our usual coordination," Kalin said at a briefing in Ankara.
According to Kalin, this week a military delegation from the United States will arrive in Turkey, and the coordination in Syria will also be discussed with them.
Earlier Turkish President Tayyip Erdogan announced that Ankara was ready to launch an operation in Syrian Manbij against the Kurdish formations. He later said that he had decided to postpone the start of the military operation in Syria after a telephone conversation with Trump on December 14, at the end of which Trump decided to withdraw US troops from Syria.