"The president underscored that a united Gulf Cooperation Council is critical to defeating terrorism and promoting regional stability".
Trump's broadside came as Kuwait's ruler flew to Saudi Arabia in a bid to resolve the worst diplomatic crisis to hit the Arab world in years.
Saudi Arabia, the powerhouse among those cutting ties to Qatar, said it did so due to the country's "embrace of various terrorist and sectarian groups aimed at destabilizing the region", including the Muslim Brotherhood, al Qaeda, the Islamic State of Iraq and Syria (ISIS) and militants supported by Iran in the kingdom's restive Eastern Province.
Trump on Tuesday hinted that the "hard line" with Qatar was partly a result of his tour of the region in May.
Trump's tweet appeared at odds with comments from US officials who had said on Monday that the United States would quietly try to calm the waters between Saudi Arabia and Qatar because Qatar is too important to USA military and diplomatic interests to be isolated. Mr Trump said on Twitter, claiming his visit to Saudi Arabia was "already paying off". "Perhaps this will be the beginning of the end to the horror of terrorism!"
On Tuesday, Trump tweeted criticism of Qatar that mirrors that of the Saudis and others in the region who have long objected to Qatar's foreign policy. That's despite accusations that Saudi Arabia, too, finances terrorism.
The Saudi Arabian, UAE and Bahraini governments have forbidden their citizens from travelling to Qatar, residing there or passing through it.
Separately, the Pentagon thanked Qatar for hosting the largest U.S. air force base in the Middle East.
Well, what was the impetus behind a series of countries' (particularly Saudi Arabia's), stance against Doha?
Qatari Foreign Minister Sheikh Mohammed Bin Abdulrahman al-Thani told the broadcaster that the Federal Bureau of Investigation has confirmed the hack and the planting of fake news.
The rift comes less than a month after Trump visited Saudi Arabia and called for Muslim nations to unite against extremism. The reports also have it that Doha has also decided not to retaliate against the measures.
Corker, who has previously said he wished Trump's iPhone would be taken away from him, emphasized the importance of the major USA air base in Qatar "to the activities we have going on in the region".
Intelligence gathered by American authorities investigating the alleged hack told the news outlet Russian hackers were to be blamed for posting the fake news attributing false statements to Qatar's Emir Sheikh Tamim bin Hamad Al Thani.
He name-checked "support of extremist groups", "hostile media" and "interference in affairs of other countries" as things Qatar would have to change if it wished to restore ties.
The United Arab Emirates has banned people from publishing expressions of sympathy towards Qatar and will punish offenders with a jail term of up to 15 years, the UAE-based newspaper Gulf News and pan-Arab channel Al-Arabiya have reported.