SINGAPORE (Reuters) -The U.S. dollar firmed slightly on Monday as anxious investors sought safety, although the moves were muted so far suggesting markets were waiting for Iran's response to U.S. attacks on its nuclear sites that have exacerbated tension in the Middle East.

The major moves were in the oil market, with oil prices hitting a five-month high, while global stocks slipped in the first market reaction to the U.S. attacks over the weekend.

In currency markets, the dollar advanced broadly against most rivals. It was up 0.25% against the Japanese yen at 146.415 after touching a one-month high earlier in the session.

The euro was 0.33% lower at $1.1484, while the Australian dollar, often seen as risk proxy, weakened 0.2% to $0.6437, hovering near its lowest level in over three weeks.

That left the dollar index, which measures the U.S. currency against six other units, 0.12% higher at 99.037. Sterling was 0.25% lower at $1.34175, while the New Zealand dollar also fell 0.24% to $0.5952.

Carol Kong, currency strategist at Commonwealth Bank of Australia, said the markets are in wait-and-see mode on how Iran responds, with more worries about the positive inflationary impact of the conflict than the negative economic impact. 

"The currency markets will be at the mercy of comments and actions from the Iranian, Israeli and U.S. governments. The risks are clearly skewed to further upside in the safe haven currencies if the parties escalate the conflict."

Iran vowed to defend itself a day after the U.S. dropped 30,000-pound bunker-buster bombs onto the mountain above Iran's Fordow nuclear site. American leaders urged Tehran to stand down while pockets of anti-war protests emerged in U.S. cities.

In a step towards what is widely seen as Iran's most effective threat to hurt the West, its parliament approved a move to close the Strait of Hormuz. Nearly a quarter of global oil shipments pass through the narrow waters that Iran shares with Oman and the United Arab Emirates.

"Markets appear to be treating the U.S. strikes on Iran as a contained event for now, rather than the start of a broader war," said Charu Chanana, chief investment strategist at Saxo.

"The muted haven flows suggest investors are still assuming this is a one-off escalation, not a disruption to global oil supply or trade."

While the dollar has reprised its role as a safe haven due to the rapid escalation in geopolitical tension, the relatively muted moves suggested investors remain wary of going all in on the greenback.

The U.S. currency has dropped 8.6% this year against its major rivals as economic uncertainty from President Donald Trump's tariffs and concern over their impact on U.S. growth has led to investors scurrying for alternatives.

In cryptocurrencies, bitcoin was up 1.3% in early trading after dropping about 4% on Sunday, while ether rose 2.3% on Monday after sliding 9% in the previous session.