"Iran will be asked to participate. Now, whether they come or not, that's up to Iranian leaders," State Department Spokesman John Kirby said on Tuesday, Reuters reported.
Kirby said about a dozen participants were expected in Vienna for the next round of discussions on Syria.
"There will be bilateral and multilateral discussions in Vienna on Friday and participation is very much still being worked (on)," Kirby said.
He said US Secretary of State John Kerry will travel to Vienna, and from there he will head to Central Asia for discussions with counterparts from Kyrgyzstan, Uzbekistan, Kazakhstan, Tajikistan and Turkmenistan.
Syria has been in a state of civil war since 2011. Syrian army has been fighting several foreign-backed terrorist groups, including ISIL.
The conflict is estimated to have claimed more than 240,000 lives so far.
Also, more than 7.2 million Syrians have been internally displaced and more than four million others have been forced to flee to neighboring countries.