The United States has stepped up its military support for Saudi Arabia over the past few months following missile strikes on the kingdom by the Yemeni Houthi group, Western diplomats said, an indication that Washington is trying to mend its strained ties with traditional Gulf allies. The desire for improved relations has been made more pressing by the Russian invasion of Ukraine last month, which has led to economic sanctions on Moscow by Washington, the European Union and others. The United States and other Western countries have been trying to persuade Saudi Arabia, the world’s top oil expor…