The ruling coalition has decided not to extend the Diet session, which means the Upper House election will almost certainly be held on July 21, senior lawmakers said.

The Liberal Democratic Party and its junior partner, New Komeito, have concluded it is unnecessary to keep the Diet open beyond the session's closing date of June 26 now that it has paved the way for passing key bills, including one on vote-value disparities, the lawmakers said Saturday.

The terms of half of the members of the House of Councilors will expire on July 28. Given the minimum amount of time required between the announcement of the election date and election day, the Upper House poll will thus almost certainly take place on July 21, the lawmakers said.

Prime Minister Shinzo Abe, who heads the conservative LDP, is already drawing up election strategies predicated on the assumption that he won't need to extend the Diet session, one of the senior lawmakers said.

On Saturday, LDP Secretary General Shigeru Ishiba said in a speech in the city of Saga that the upcoming poll will be announced July 4 and the nation will go to the polls on July 21, "unless extraordinary circumstances arise."