The United States has strongly condemned the May military takeover and repeatedly called for a swift return to democracy after the army seized power following months of protests against Ms Yingluck's elected government.
On January 26, US Assistant Secretary of State for East Asian and Pacific Affairs Mr Daniel Russel met Yingluck as part of the Thai leg of a Southeast Asia trip in which he also held talks with government officials and civil society representatives in the capital.
In a speech delivered at Chulalongkorn University in Bangkok he said "the perception of fairness is important", three days after Yingluck was impeached by a junta-stacked parliament and prosecutors announced corruption charges that could see her jailed for 10 years.
"When an elected leader is deposed, impeached by the authorities that implemented the coup, and then targeted with criminal charges while basic democratic processes and institutions are interrupted, the international community is left with the impression that these steps could be politically driven," he said.
Mr Russel stressed that the US was not picking sides in Thai politics but advocating a "more inclusive political process".
He also repeated the US call for an end to martial law and restrictions on free speech and assembly.
US State Department spokeswoman Ms Jen Psaki said that in talks with Foreign Minister Mr Tanasak Patimapragorn, Mr Russel had "underlined that our relationship with Thailand cannot return to normal until democracy is re-established".
Since seizing power the military has suspended democracy and curtailed freedom of expression in the kingdom, responding aggressively to any form of protest. Under martial law, political gatherings are banned.
Washington suspended $4.7 million in security-related aid to Thailand, roughly half of its annual assistance to the longtime ally, after the military takeover.
It had also considered moving annual military exercises outside the kingdom but later said the US would go-ahead with a "scaled-down" version of the Cobra Gold joint drills, which begin next month.
A US embassy spokeswoman confirmed that Mr Russel did not meet junta leader Prayut Chan-O-Cha, who was appointed Thai premier after the coup, during his official visit.
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