Russia says it is launching a "full embargo" on most food imports from the United States, the European Union, Australia, Canada, and Norway.
The embargo -- which will affect the import of beef, pork, poultry, fish, fruit, vegetables, cheese, milk, and other dairy products -- is in retaliation for Western sanctions imposed against Moscow for its perceived support of rebels in eastern Ukraine as well as the annexation of Crimea.
The moves were announced on August 7 by Prime Minister Dmitry Medvedev during televised remarks at a government meeting. He said the decision was taken on orders from President Vladimir Putin.
"There is nothing good in sanctions and it wasn't an easy decision to take, but we had to do it," Medvedev said.
The sanctions do not include baby food or products purchased by Russians when abroad.
The ban is valid immediately and will last for one year.
"But if our partners display a constructive approach toward cooperation," he added, "then the Russian government will be ready to revise the terms of the imposed measures."
The European Union's executive warned on August 7 that it is ready "to take action" over the Russian decision.
In a statement, the European Commission said, "This announcement is clearly politically motivated. Following full assessment by the commission of the Russian Federation's measures, we reserve the right to take action as appropriate."
A commission spokesman refused to give further details on what action the EU might consider.
Swedish Foreign Minister Carl Bildt tweeted on August 7: "President Putin has decided that Russia's consumers should have more expensive and less quality food. Great idea...??"
Medvedev said the move would bolster Russia's domestic agriculture.
Russia buys fruit and vegetables from the EU worth an annual 2 billion euros ($2.8 billion) and food and agricultural products from the United States worth about $1.4 billion.
The United States had said on August 6 that any such move would only deepen Russia's isolation from the international community.
White House spokeswoman Laura Lucas Magnuson said that retaliation by Moscow against Western companies or countries for sanctions imposed earlier by Washington and the European Union will cause further damage to Russia's economy.
She noted that the Russian Central Bank had previously said that a ban on food imports would increase inflation in Russia.
Medvedev said on August 7 that Russia is also considering a "serious measure" banning Western air carriers from flying over Russia on flights to and from Asia.
Any such move would significantly increase costs and lengthen flight times.
Medvedev said a final decision on whether to ban the flights by EU and U.S. airlines had not been taken, but he said Russia has decided to ban transit flights for Ukrainian airlines via its territory.
The low-cost Russian airline Dobrolyot stopped flying recently after being sanctioned by the European Union.
Medvedev also said Russia may introduce restrictions regarding the imports of planes, naval vessels, and cars.
On August 5, Putin said the government should make sure any retaliatory measures against the EU and the United States did not hurt Russian consumers.
Moscow has already imposed bans on certain agricultural imports from Ukraine, Moldova, and several EU countries, including Poland.
The Russian bans follow the latest round of sanctions imposed by the United States and the EU last month, which for the first time targeted entire sectors of the Russian economy.
The sanctions target Russia's oil and defense industries and limit the access of state-owned Russian banks to Western financial markets.