The White House on Wednesday declined to set a deadline for the U.S.-Iran nuclear talks, saying Tehran is expected to present more details on its negotiating position within weeks.

"Diplomacy is always his (President Donald Trump's) first option," White House Press Secretary Karoline Leavitt said at a daily briefing. However, she added that "there are many reasons and arguments that one could make for a strike against Iran."

Iran is expected to submit a written proposal on how to resolve its stand-off with the United States in the wake of U.S.-Iran talks in Geneva, Reuters quoted a senior U.S. official as saying on Wednesday.

A Trump adviser said the White House is moving closer to possible military actions, estimating a "90 percent chance" of strikes within weeks if talks fail, Axios reported Tuesday.

Any U.S. operation could involve a large-scale, weeks-long campaign, potentially conducted jointly with Israel, targeting Iran's nuclear and missile programs and posing a major threat to Tehran's leadership, said the report, quoting sources familiar with the matter.

According to a U.S. media outlet, the U.S. military could be ready to carry out strikes against Iran as soon as this weekend, but Trump has not yet made a definitive call on whether to approve the operation.

Israel is on heightened alert and assessing that a confrontation with Iran could begin "soon," state broadcaster Kan reported Wednesday, citing senior Israeli officials.

The report said Israel is maintaining a high level of readiness amid the possibility of a near-term U.S. strike on Iran, estimating that if launched, such an operation could develop into a weeks-long campaign.

Officials said Trump appears closer to launching a large-scale confrontation in the Middle East, and that Israel is preparing for a scenario in which fighting could break out "possibly within days."

(With input from agencies)