In April 1981, the Israeli Air Force attacked Syrian forces in Lebanon to prevent them from seizing the strategic Sannin ridge. Syria responded by deploying surface-to-air missiles into the Biqa‘ Valley, threatening Israel’s ability to monitor PLO forces in Lebanon. To avert war, Reagan sent emissary Philip Habib to the Middle East, but he failed to persuade the Syrians to withdraw the missiles. When fighting escalated between Israel and the PLO that July, the Reagan administration feared that Israel would invade Lebanon. Ultimately, Habib managed to negotiate a de facto ceasefire between Israel and the PLO.
