WASHINGTON — Britain will add its voice to President Obama’s in discouraging an Israeli military strike on Iran when Prime Minister David Cameron begins a three-day visit here this week, a senior British diplomat said Monday.
Prime Minister David Cameron, at 10 Downing Street on Monday, is coming to the United States for a three-day visit.
“The prime minister is pretty clear that he does not think military action against Iran would be helpful,” the diplomat, Peter Westmacott, Britain’s recently appointed ambassador to the United States, told reporters. “We do not regard that as the right way forward in the months to come.”
Mr. Cameron, he said, supports Mr. Obama’s vow that Iran will not be allowed to acquire nuclear weapons. And, like the president, the prime minister believes military force must be preserved as an option. But an Israeli strike, Mr. Westmacott said, could “unleash a whole variety of different consequences” and might backfire by strengthening the Iranian regime and the resolve of the Iranian people to acquire nuclear status.
“We are, all of us, concerned about what might flow from a decision to take precipitate military action,” he said.
Mr. Cameron, in his talks with Mr. Obama, is expected to press for tighter diplomatic and economic sanctions, said a senior British official in London. “There’s a lot more to be done to turn up the pressure, to turn up the dial,” said the official, who spoke on condition of anonymity to discuss the talks with the White House.
Speaking to reporters on Monday, Mr. Cameron said, “The Iranian situation is vital, in terms of trying to demonstrate to the world, and in particular to the Iranians, our continued road of sanctions, the pressure that’s got further to run, and that we’re going to push that as hard as we can.”
Mr. Cameron is to arrive in the United States on Tuesday, a week after Prime Minister Benjamin Netanyahu of Israel traveled to Washington to rally American support for a potential military confrontation with Iran. While Mr. Netanyahu told Mr. Obama that Israel had not decided to carry out an attack, administration officials said, he expressed fears that the window for diplomacy and sanctions was closing.
Mr. Obama urged Mr. Netanyahu not to give up on nonmilitary options, though he reaffirmed Israel’s sovereign right to defend itself, and he explicitly renounced a policy of containing a nuclear-armed Iran. Prime Minister Cameron, Mr. Westmacott said, agreed with that policy.
Britain has been less fixated than the United States on talk of war with Iran, in part because of the American presidential election campaign, in which Republicans candidates have criticized Mr. Obama’s policy as not being tough enough on Tehran. Supporters of Israel gathered last week in Washington for a conference of the pro-Israel lobbying group the American Israel Public Affairs Committee.
Mr. Cameron said he believed that Mr. Obama’s warnings during Mr. Netanyahu’s visit about the consequences of an Israeli strike on Iran had “changed the situation,” in terms of its likelihood. As for Britain, he said, “We’ve been very clear: If there was an Israeli strike, we wouldn’t support them.”
Britain’s voice is important because the nation is a close ally of the United States in dealing with Iran, as well as other regional trouble spots, including Syria, where its diplomatic role is central. Britain currently holds the rotating chairmanship of the United Nations Security Council, which has struggled to pass a resolution that would halt President Bashar al-Assad’s deadly attacks on civilians in Homs.
Mr. Westmacott made clear that Britain would not lead any effort to arm Syrian rebels or marshal a military intervention in the country. Lacking a consensus in the Security Council, with Russia continuing to oppose military action, he said there was no mandate to act. And he said that taking on Syria, with robust air defenses and a well-trained army, would require a much greater level of force than the Libya action had.
“The conditions are not the same,” Mr. Westmacott said. Intervening in Syria, he said, would require “a very substantial commitment of equipment and of troops.”
Mr. Obama, returning the hospitality he received on his visit to Britain last May, plans to give Mr. Cameron full ruffles and flourishes, with a state dinner at the White House on Wednesday. But the highlight may be a road trip to Dayton, Ohio, where the two leaders will watch a first-round game in the N.C.A.A. basketball tournament, featuring Western Kentucky and Mississippi Valley State.
The game was the White House’s idea, Mr. Westmacott said, adding that Mr. Cameron was familiarizing himself with March Madness. He will presumably also get a primer on the value of visiting Ohio, a swing state, in an election year.
