RIO DE JANEIRO (Reuters) -Canada, Benin, France and Jamaica have offered support to a U.N.-backed international security force aimed at tackling rampant gang violence in Haiti, according to a statement from the United States, which co-hosted a meeting on the mission with Brazil. Washington has pledged $200 million to fund the Multinational Security Support (MSS), which Kenya stepped forward to lead last year. U.S. Secretary of State Antony Blinken gathered officials in Rio de Janeiro, where foreign ministers of the G20 group of developed nations are meeting this week, and urged support for t...