The embassy said it would make an announcement when it was ready to reopen.
The detentions came as the U.S. Embassy in Ankara was closed on Monday due to an unspecified security threat.
The notice also advised U.S. citizens in Turkey should avoid large crowds, keep a low profile and otherwise be cautious.More news: S. Africa recalls meat products after listeria outbreak
The four suspects detained were all Iraqi citizens and were taken to the police station for legal proceedings, state-run Anadolu Agency reported.
Turkey police force has detained 12 suspected Islamic State extremists amid ongoing crackdown and closure of U.S. embassy.
"Both the intelligence service and security forces have taken extra measures, and important results have been achieved", he said, without elaborating.
Meanwhile, Deputy Prime Minister Bekir Bozdağ said that Turkey is the country most effectively fighting against Daesh. Moreover, 12,538 suspects, including 5,654 foreigners, were detained between 2011 and 2018 for links to Daesh. The source said that the arrested suspects, who are Iraqi nationals, were supposedly recruiting members for the terror group and were in contact with conflict zones.More news: Amazon Could Soon Offer Checking Accounts
In 2013, a suicide bomber detonated an explosive in front of the U.S. Embassy in Ankara.
Turkish authorities have detained several suspects on charges of plotting an attack. Of this figure, the ministry said that five were captured, eight surrendered and seven were killed, including a regional leader of the Kurdistan Workers' Party, a separatist militant group that has waged a violent insurgency against the Turkish state for four decades.
The Turkish capital saw a wave of attacks in 2015 and 2016 in which hundreds were killed.More news: Brazil's Neymar sidelined with foot surgery