Republicans have stepped up pressure on US President Joe Biden to end talks on the Iran nuclear deal over Tehran's support for Hamas, the militant group that governs the Gaza Strip.
The US has been holding indirect talks with Iran in Vienna in a bid to return to the 2015 accord that constrained Iran's nuclear programme. Donald Trump, the former US president, withdrew from the deal and imposed sweeping sanctions.
In a letter to Biden, more than 40 Republican senators wrote: "Palestinian terrorists in Gaza, who are funded by Iran, have launched a series of rocket attacks into Israel.
"They are targeting Israeli civilians and cities, including Israel's capital Jerusalem. This is troubling as members of your administration are currently in Vienna negotiating with Iran, the world's leading state sponsor of terrorism."
The Republicans called on Biden to "immediately end negotiations with Iran" and "make clear that sanctions relief will not be provided".
The US president has argued that the 2015 accord, negotiated under Barack Obama's administration, had previously been working. The talks in Austria, through European intermediaries, have been held up by Iran's demands that Biden lift all sanctions imposed by Trump.
Biden has sought to move the focus of US foreign policy away from the Middle East to China and waited until Wednesday to make his first comment on the new crisis unfolding in Gaza. He said he had spoken to Benjamin Netanyahu, the Israeli prime minister, and backed Israel's right to defend itself, while also calling for peace.
Republicans criticised his hesitancy, and the fact he has not yet appointed an ambassador to Israel. Mike Pompeo, Trump's former secretary of state, accused him of "emboldening terrorists".
Biden also faced a backlash within his own party. Alexandria Ocasio-Cortez, New York's Democrat representative in Congress, said his position on the Gaza conflict had served to "dehumanise Palestinians and imply the US will look the other way at human rights violations".
She added: "It's wrong. Biden reinforces the false idea that Palestinians instigated this cycle of violence. This is not neutral language. It takes a side - the side of occupation."
The White House defended its level of engagement in the crisis. A spokesman said officials had made more than two dozen phone calls to lsraeli and Palestinian counterparts, and other leaders in the region.
Joe Lieberman, the former Democrat senator from Connecticut, said: "We're engaged in the Middle East whether we like it or not. So we might as well acknowledge that and try to be engaged in the most constructive, strong and substantive way. Time is of the essence now."
Tony Blinken, the US secretary of state, said he had spoken to Mahmoud Abbas, the Palestinian president, calling for an end to rocket attacks.
Blinken said: "I spoke with President Abbas about the ongoing situation in Jerusalem, the West Bank and Gaza. I expressed condolences for the loss of life. I emphasised the need to end rocket attacks and de-escalate tensions."
The state department added: "The secretary also expressed his belief that Palestinians and Israelis deserve equal measures of freedom, dignity, security and prosperity."