Erdogan called the indictment "scandalous" and said his security detail was protecting him against Kurdish militants protesting outside his ambassador's residence.
Erdogan's talks with Serbian President Aleksandar Vucic focused on trade and investment, but also covered political relations in the region, where many countries have historic and religious links with Turkey from centuries of Ottoman rule.
According to Nauert, Turkish authorities summoned the third employee, but the person of interest has not been formally arrested yet.
In a blunt and personal criticism directed at Bass, Erdogan said the USA envoy acted unilaterally in suspending US visa services in Turkey after the arrest of Topuz.
Meanwhile, Bass denied Turkish press reports alleging that a second US consulate employee was hiding inside after an arrest warrant was issued against him, saying that "no one is hiding in any of our facilities".
In the 1990s, Turkey backed Bosnian Muslims in the war that pitted them against the Orthodox Christian Serbs and Catholic Croats.
Erdogan said the $800 million of trade between the two countries "is not enough" and that it should increase sharply in the near future. Serbia was ruled for nearly 500 years by the Ottoman Empire.
President Recep Tayyip Erdoğan's three-day visit to Serbia-- the first at this level since 2007 - carries considerable importance for bilateral relations and will influence regional stability, Serbia's ambassador to Turkey told Anadolu Agency (AA).
He was referring to Metin Topuz, a veteran Turkish employee of the USA consulate in Istanbul, who was detained last week for alleged link with the US -based cleric Fethullah Gulen, blamed by Ankara for having masterminded the failed coup in July 2016. A banner in Novi Pazar on Wednesday showed Gulen dressed in a prison uniform. He said Turkey and Serbia share common views. "We will preserve our friendship".