Company claims units were bought at prices significantly above market value.
The Saudi crown prince will hold talks with Kuwaiti Emir Sheikh Sabah al-Ahmad al-Jaber al-Sabah, the Kuwaiti News Agency said in a tweet.
Erdogan said Qatar's emir had donated the plane, which he said was worth around US$500 million, to the Turkish state after hearing that Turkey had expressed interest in buying it.
Qatar plans to invest in the car, high-tech and banking sectors - three traditional strengths of the German economy.
US$1 billion will be in the form of loans and the rest will be invested in projects in the war-battered country.
Analyst says Philippine military declining to name the two, perhaps to avoid embarrassment that Malaysian militant Amin escaped Marawi.
Najib Razak says although Malaysia enjoys special relationship with Saudi Arabia, it has good cooperation with all countries.
Foreign minister denies report that the two had disagreed over the Qatari Emir's upcoming state visit.