* U.S., China set to slap new tariffs on imports this week
* China manufacturing sector cools slightly, new orders fall
* Mexico left-wing candidate wins presidential race
By Karin Strohecker
LONDON, July 2 (Reuters) - A cocktail of soft Chinese data, trade jitters and political tensions in Europe tipped emerging market assets back into selloff mode on Monday with stocks falling more than 1 percent and currencies chalking up losses.
Mexico's peso fell in line with broader markets, more than offsetting early gains after leftist Andres Manuel Lopez Obrador won, as expected, a presidential election decisively and looks on track to achieve a congressional majority.
In a victory speech Lopez Obrador struck a conciliatory tone, saying he would preserve fiscal discipline and central bank independence but also added he would review oil contracts awarded to major oil companies to ensure there had been no corruption.
"The win has the potential to bring profound changes in Mexico's economic policy and politics," BlackRock wrote in a note to clients, adding it expected markets to rebound from their depressed level in the near term.
"(Lopex Obrador's) victory represents a blow to a political establishment tainted by corruption charges, rising crime and persistent inequality, and suggests the forces of populism have not yet peaked around the world."
Elsewhere, data over the weekend showed China's manufacturing sector cooled slightly in June as firms faced rising input costs and a fall in export orders amid an escalating trade dispute with the United States.
Markets were also nervous about a deepening row over migration policy in the German coalition government.
Adding to the woes was investors' concern over the trade tensions, with the United States and China set to impose new tariffs on each other's imports this week and both sides threatening more if the other doesn't back down.
"Emerging markets are likely to continue to be jack-hammered by that trade threat considering for many the U.S. is still at the end of their supply chains," Rabobank analysts said in a note to clients.
MSCI's emerging market equity index fell nearly 1 percent, with Asian markets suffering badly. Some Chinese mainland indexes closed nearly 3 percent lower while the benchmark of export giant South Korea slipped 2.4 percent - all to their lowest level in around a year.
Purchasing managers' data from other emerging markets painted a mixed picture. Turkish, Russian and South African manufacturing activity contracted in June, hit by slowing new orders . However, in central Europe both Poland and Czech data was better than expected, the former recording its best performance in five months.
Other currencies fared little better with the dollar index crawling higher while China's yuan on- and offshore weakened past 6.66 to the dollar for the first time since November. South Africa's rand and Turkey's lira were both around 0.5 percent weaker.
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Reporting by Karin Strohecker, additional reporting and graphic by Claire Milhench; editing by David Stamp