TEHRAN, Young Journalists Club (YJC) - "Qatar has pledged $15 billion of direct investments in Turkey," presidential spokesman Ibrahim Kalin wrote on Twitter.
"Turkish-Qatari relations are based on solid foundations of true friendship and solidarity," he said.
The announcement came after Qatar's emir Sheikh Tamim bin Hamad Al-Thani held lunchtime talks with Turkish President Recep Tayyip Erdogan.
Erdogan thanked the emir and the people of Qatar for "standing by Turkey," the official Anadolu news agency reported.
He said relations with Qatar, which he described as a "friendly and brotherly country," would be boosted in many areas.
Turkish Finance Minister Berat Albayrak, who is Erdogan's son-in-law, and his Qatari counterpart Ali Sharif Al-Emadi were present at the talks in the capital Ankara.
Turkey has been rocked in recent days by a sharp decline in the value of its lira after US President Donald Trump tweeted last Friday that Washington was doubling aluminium and steel tariffs for Ankara.
Washington's move came during an ongoing dispute over Turkey's holding of an American pastor for two years.
In response, Erdogan has called for a boycott of US electrical goods while Ankara has sharply hiked tariffs on some US goods.
The turmoil has raised fears of a looming economic crisis in Turkey and prompted alarm that foreign investors in the country, including Qatar, could be hit in the fallout.
Turkey and Qatar -- which is also a very close US ally -- have become close economic and political partners in recent times.
Doha has $20 billion worth of investments in Turkey, official figures showed last month, and Ankara is now one of the top exporters to the emirate.
In recent days, Qatari supporters of Turkey have begun a public campaign in Doha to change their riyals into lira in an attempt to shore up the plunging Turkish currency.