JERUSALEM, Israel -- The U.S. and Israel postponed what would have been their largest-ever joint missile defense drill, scheduled for this spring.

By delaying the major military exercise with Israel, the U.S. appears to be trying to avoid further tensions with Iran over its nuclear program, which one U.S. official said would demonstrate the Obama administration's commitment to Israel's security.

Reports say Washington was concerned the exercise could lead to an escalation with Iran. The drill, called Austere Challenge, would have simulated an Iranian or other missile attack against the Jewish state.

Officials said the exercise may still take place later this year, but one Israeli expert said it was shocking to cancel a missile defense drill intended to "reassure Israel and instill confidence in Jerusalem."

Over the weekend, a senior Israeli official criticized President Obama for going soft on Iran, following the Senate's unanimous vote to impose more sanctions.

"In the U.S. administration, there is hesitation [to impose the sanctions] for fear of oil prices rising this year, out of election-year considerations," Israeli Strategic Affairs Minister Moshe Ya'alon said.

The comments come as some say international sanctions against Iran are starting to bite.

Israeli Prime Minister Benjamin Netanyahu said the Islamic Republic is beginning to wobble under the sanctions and threats against its central bank.

Still, the U.S. is concerned Israel might be preparing to attack Iran.

Top U.S. military commander Gen. Martin Dempsey is due to arrive in Israel Thursday for talks, with Iran expected to top the agenda.

The visit will be his first official trip since becoming chairman of the Joint Chiefs of Staff, Sept. 30.