WASHINGTON--A Soviet freighters route to Nicaragua may be carrying advanced MiG-21 jet fighters, according to U.S. intelligence officials quoted by CBS news.

Although there is no hard proof, satellite photographs show that when the ship was loaded a dozen crates similar to those used to transport MiG-21's disappeared from a Black Sea pier, CBS said.

The Nicaraguan embassy denied the reports. But White House Deputy Press Secretary Larry Speaks said the U.S. has not ruled "anything out," including a possible blockade of Nicaragua. Other U.S. reports suggested that the Soviet Union is also sending over attack and transport helicopters.