Months after Turkey shot down a Russian fighter jet supposedly trespassing its airspace, the relationship between the two countries are not getting any better.

In a statement released on Thursday, the Russian defence ministry accused Turkey of plotting to invade Syria.

"We have serious grounds to suspect Turkey is in intensive preparations for an armed invasion of the territory of a sovereign state—the Syrian Arab Republic," the ministry said in a statement, as quoted by Yahoo! News.

Moscow also said Ankara is trying "to conceal illegal military activities at the Syrian border," which supposedly involves the "presence of troops and military equipment."

"We are recording more and more signs of covert preparations by the Turkish armed forces for active action on Syrian territory," the defence ministry said.

On Friday, however, Turkish President Recep Tayyip Erdogan dismissed Russia's accusations, and turned the tables on Moscow.

"I find this Russian statement laughable... rather it is Russia that is currently engaged in an invasion of Syria," Erdogan said, quoted by the state-run Anatolia news agency.

"Turkey does not have any plans or thoughts of staging a military campaign or ground incursion in Syria," the Turkish leader added.

Erdogan said Russia should instead be held accountable for the estimated 400,000 people its forces have allegedly killed in Syria, in connivance with Syrian President Bashar al-Assad.

Moscow is also supposedly trying to set up a "boutique state" for Assad, according to the Turkish president.

"Turkey is part of a coalition, is working with its allies, and will continue to do so. As we have repeatedly said, Turkey will not act unilaterally," Erdogan said.

In a related news, Saudi Arabia has also said that it is prepared to join ground operations against the Islamic State (ISIS), if the United States will initiate it.

"The kingdom is now ready to participate in any ground operations that the coalition (against Islamic State) may agree to carry out in Syria," said Saudi defence minister Brigadier General Ahmed Asseri, as quoted by The Daily Express.