Topuz was arrested on terrorism charges, but little else is known about the allegations against him. US Ambassador John Bass complained Wednesday that Turkey had left the United States in the dark as to why he was detained.
"There are ... times that our two governments do not seem to be eye to eye (on) specific aspects of our bilateral relationship. We are observing one of those this week as a result of actions the Turkish government took against some of our local staff," Bass said at a news conference in Ankara.
He said it was difficult to comment on Topuz's case "because again there has been no official communication from the Turkish government regarding these matters for the ostensible evidences."
He added that accusing US consular employees of terror-related crimes was "a very serious allegation."
His comments are the latest in a terse exchange of words to mark deteriorating relations between the United States and Turkey.
Turkish Foreign Minister Mevlut Cavusoglu spoke to US Secretary of State Rex Tillerson on Wednesday for the first time since the visa crisis began, Turkish foreign ministry sources told CNN.
State Department spokeswoman Heather Nauert said Tillerson "conveyed to the foreign minister his profound concern over the detentions of Turkish national employees of our diplomatic mission to Turkey and of several American citizens."
The two NATO allies have feuded over several issues, including the United States' refusal to extradite Muslim cleric Fethullah Gulen. Gulen lives in exile in Pennsylvania and Turkey blames him for coordinating an attempted military coup last year.
There have also been complaints by Ankara over Washington's support for Kurdish fighters in Syria. Ankara considers them terrorists while Washington sees them as the backbone of Syria's anti-ISIS forces.
And now a string of arrests of US citizens -- as well as Turkish nationals working for the US mission -- has become a new wedge between the countries.
Erdogan snubs Bass
Washington's visa freeze has caused ire in Ankara, and Bass' comments come a day after President Erdogan said he would no longer recognize Bass as the US' representative. Bass is an outgoing ambassador and will soon take up a new post in Afghanistan.
"In fact, this ambassador is doing his farewell visits," Ergodan said Tuesday.
"And right now, be it our Cabinet ministers, parliament head -- and I personally am not accepting his farewell visit, and will not do so, because we do not see him as a representative of the United States in Turkey -- let me say that clearly."
But Bass defended the visa freeze Wednesday as a necessary measure while trying to calm the waters.
"It is important to reiterate that it was not a decision we took lightly....
Read More: US ambassador to Turkey slams Ankara over staff arrest