* Yen gains as riskier trades unwound on swine flu worries
* Dollar climbs steeply vs Aussie, kiwi and euro
* Mexican peso falls 2 percent vs dollar
By Charlotte Cooper
TOKYO, April 27 (Reuters) - The yen and the dollar rose on Monday and the Mexican peso fell on concern about the spread of swine flu, which has killed 103 people in Mexico and infected people in the United States and Canada.
The World Health Organisation declared the flu a "public health emergency of international concern" that could become a pandemic or global outbreak of serious disease.
The Mexican peso fell 2 percent against the dollar in Asian trade, although Mexican Finance Minister Agustin Carstens tried to reassure markets, saying the impact on economy would be "transitory"..
The dollar dropped to its lowest in a month against the Japanese currency but climbed against the Australian and New Zealand dollars and edged higher against the euro.
Analysts said investors were unwinding positions in currencies such as the New Zealand dollar, where a teacher was being treated for flu-like symptoms, and were cautious about the economic impact on travel and transport.
"Swine flu is centre stage. The Aussie and kiwi are hit hard. There is general risk aversion with concerns about the possible expansion to other countries," said Masafumi Yamamoto, head of FX strategy Japan, at Royal Bank of Scotland.
The peso weakened past 13.60 per dollar from a close of 13.284 pesos on Friday and Yamamoto said it would face further pressure later in the day when U.S. trading began.
The dollar dropped to 96.62 yen, its lowest in a month, before edging back to 96.75 yen, down 0.4 percent on the day.
The euro fell 1.3 percent to 127.05 yen and dropped 0.5 percent to $1.3161.
The New Zealand dollar shed 1.4 percent to $0.5640 and the Australian dollar fell 1.5 percent to $0.7121. Both were down more than 1 percent against the yen.
Australia said it would strengthen its border surveillance for swine flu. See for latest wrapup.
Takahide Nagasaki, chief FX strategist at Daiwa Securities SMBC in Tokyo, said the market needed to see the extent of the outbreak and its overall impact before any judgments could be made on the broader market effect.
"What needs to be watched going forward is the kind of impact the outbreak will have on North American trade and the movement of people," Nagasaki said. (Additional reporting by Shinichi Saoshiro; Editing by Edwina Gibbs)