"You've now become a very big advocate, and we appreciate it", Trump told Sheikh Tamim bin Hamad Al Thani.
But the USA president has since softened his language against Doha and praised its counter-terrorism efforts.
White House spokeswoman Sarah Huckabee Sanders said last week that Sheikh Tamim bin Hamad Al Thani will be meeting with Trump on April 10.
Kulankan ayaa lagu beegay todobaadyo kadib kulankii dhexmaray Dhaxal-sugaha Sacuudiga Maxamed Bin Salmaan oo isaguna asbuucyadii lasoo dhaafay ku sugnaa dalka Maraykanka.
One veteran congressional foreign policy adviser who works closely on the Qatar issue said the upcoming Oval Office meeting should serve as a frank wake-up call to the emir. Qatar denies the allegations and says the moves attempt to undermine its sovereignty.
"President Trump and the Emir are going to have a lot to talk about, and the Qataris are going to hear the same thing on the Hill they'll hear in the White House", said the source, who was not authorized to speak on record. "We have to stop the funding of terrorism".
When the Persian Gulf crisis erupted last summer, Trump was initially sympathetic to concerns voiced by Saudi Arabia, the UAE, Bahrain and Egypt who accused Qatar of spreading extremism, fomenting opposition in the region and cozying up to Iran.
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Trump hasn't repeated that cost lately and Qatar has since taken steps to deal with USA considerations.
As a warm-up to the emir's visit, the State Department approved the sale of 5,000 Advance Precision Kill Weapon Systems (APKWS) to Qatar, including 5,000 high explosive warheads. Qatar denies that charge but has taken steps to address US concerns. "The Qatari emir will have to decide if he wants to try to be a true ally of the United States or continue to support Hamas and its murderous terrorism-he can't do both".
Trump praised Qatar's military purchases, saying they buy "a lot of equipment from us, a lot of military airplanes, missiles".
Qatar has long sought to stress its role as an agreeable USA partner in a strategically vital region.
The meeting between the two leaders came after Trump in June denounced Qatar for allegedly financing terrorist groups.
Information for this article was contributed by Ken Thomas of The Associated Press.