"That (the) United States arms a terrorist group is what causes instability", Khameini wrote on Twitter Monday.
The report also warned that the al-Qaeda in the Arabian Peninsula (also outlawed in Russia) remains a security concern, as it has not abandoned the goal of attacking the Saudi government and Western entities in the country, reports Sputnik. "If we don't slap the enemy" outside our borders, Iran's public prosecutor told the public in March, "he'll come to your door".
Saudi Arabia, Bahrain and the UAE are blockading Qatar and have closed off airspace to Qatar Airways, a decision which Saudi Arabia insists has been taken to protect its citizens from "threats". Turkey and Iran have stepped into the gap, raising the specter of a reshuffling of alliances in the Gulf region.
Qatari foreign minister Mohammed bin Abdulrahman Al Thani said yesterday the country had "no clue what are the main reasons behind all these measures".
Also last month, the Saudi mission to the United Nations accused Iran of "deception" and of "supporting terrorism and threatening stability in the region".
Earlier on Monday, Zarif met and held talks with the European Union (EU)'s foreign policy chief, Federica Mogherini, on a range of issues, including the 2015 multilateral nuclear deal with Iran.
Riyadh has denied involvement in the suicide bombings and gun attacks on Iran's parliament and the mausoleum of the Islamic Republic's founder, Ayatollah Ruhollah Khomeini.
Elsewhere in his remarks, Zarif said the United States under President Donald Trump was turning a blind eye to Saudi Arabia's role in the 9/11 terrorist attacks in the USA, which killed some 3,000 people, and other attacks elsewhere in the West.
Qatar and Iran share the largest underwater natural gas field in the world.
Following Iran's Islamic revolution in 1979, both countries discontinued diplomatic relations.
The Iranian foreign minister has traveled to Norway to participate in the Oslo Forum, which gathers leading armed conflict mediation practitioners. If U.S. rates rise, Saudi Arabia is seen likely to follow suit with its rates because the country's currency is pegged to the dollar.
Trump said "states that sponsor terrorism risk falling victim to the evil they promote".
CNN's Katie Polglase and Katie Hunt contributed reporting.