* Watchdog bans imports from four U.S. plants
* Blames presence of antibiotic
* Two Smithfield Foods plants affected
* More bans could follow
* U.S. pork exports may halt on quality dispute
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By Aleksandras Budrys
MOSCOW, Dec 10 (Reuters) - Russia widened its ban on U.S. pork imports on Thursday to include four more plants and could close its market entirely to the United States should Washington fail to observe quality standards, officials said on Thursday.
Russia's farm produce watchdog said the latest ban will apply from Dec. 18 and include two plants belonging to major meat firm Smithfield Foods Inc. The watchdog's head, Sergei Dankvert, told Reuters more bans could follow.
In a separate interview, the head of an industry lobby said U.S. pork producers could face a complete halt in supplies to Russia due to delays in agreeing on meat safety certification.
"U.S. imports may halt for a certain period of time, as until now a mutually acceptable veterinary certificate has not been agreed," National Meat Association head Sergei Yushin said.
"We are not closing Russia to U.S. imports, but the technical issue of the certificate exists," he told Reuters.
Russia, among the five biggest export markets for U.S. pork, has had several trade rows with Washington over meat and poultry supplies in recent years. Moscow insists all bans are on health grounds, whereas some U.S. observers have called them political.
Russia's latest banapplies to Smithfield's slaughterhouses in Monmouth, Iowa and Clinton, North Carolina. Also banned are the Pork King Packing plant in Marengo, Illinois and Hatfield Quality Meats in Hatfield, Pennsylvania.
Rosselkhoznadzor, the watchdog, cited the presence of the antibiotic oxytetracycline as the reason for the latest ban -- the same problem that led it to ban imports from seven other U.S. plants from earlier dates in December.
Dankvert said U.S. suppliers in general were not meeting Russian standards.
"The U.S. official (Food Safety Inspection) Service (FSIS) has said it would not observe Russian food safety standards, without giving any explanation," Dankvert said.
"Therefore, since the end of October, we have intensified our monitoring of U.S. pork products," he said. "If we do blanket monitoring, or intensive monitoring, then the number of candidates for bans will increase."
Yushin, the meat association's head, also criticised Washington for failing to send a delegation to Russia to agree on the veterinary certificate, a document which accompanies meat shipments and without which imports are not possible. (Editing by Robin Paxton)