JERUSALEM, July 22 (Reuters) - The U.S. ambassador to Israel visited its bio-chemical defence laboratory and was briefed on a coronavirus vaccine prototype for which it is seeking U.S. Food and Drug Administration (FDA) regulation, a U.S. official said on Wednesday.

The vaccine being developed at the Israel Institute for Biological Research (IIBR), in rural Ness Ziona, began animal trials in March. A source familiar with IIBR activities said human trials were expected before year's end.

A U.S. official described Ambassador David Friedman's visit to the IIBR on Monday as part of the two allies' "robust fight against the coronavirus". Israel's Defence Ministry, which oversees the IIBR, had no immediate comment.

The IIBR is seeking FDA vaccine regulation, the U.S. official added. Asked whether Friedman would help in this regard, the official said only that the envoy "is working tirelessly to ensure that things that (can) help the American people can get to them in the most effective and efficient way".

The FDA website says its "regulations for the development of vaccines ensure their safety, purity, potency and effectiveness" and could pave the way for a vaccine's use in the United States. (Writing by Dan Williams Editing by Mark Heinrich)