VIENNA — UN Secretary-General Ban Ki-moon expressed optimism Thursday about the first direct talks between Israel and the Palestinians in nearly two years, while acknowledging the process could prove "very difficult."Ban called on both sides to show sincerity, flexibility and pragmatism as Prime Minister Binyamin Netanyahu and Palestinian Authority President Mahmoud Abbas were to meet in Washington later Thursday.RELATED:Opinion: Reason for optimism in talksNetanyahu: Israel committed to 'secure, durable' peaceAnalysis: US talks low-key approach in launching talks"I am very encouraged and happy by these direct talks for (the) Middle East peace process," Ban told reporters after a meeting with Austrian Foreign Minister Michael Spindelegger."I know it will not be (an) easy process — it may be very difficult and there may be some hurdles — but we must work very closely and very hard to avoid all these unexpected political or security hurdles," he said.Ban commended US President Barack Obama for his efforts. He also called on countries in the region and the international community to join forces in facilitating the Mideast peace process.He urged both Israel and the Palestinians to "work sincerely and with a sense of flexibility, a sense of pragmatism." In addition, Ban said it was important that Abbas be "given full support" and that his leadership is recognized by the international community.