President Asif Ali Zardari will attend the 25th NATO Summit in Chicago on May 20-21 at the invitation of NATO Secretary General Anders Fogh Rasmussen, the Foreign Ministry said Thursday. In Chicago, the President will address the Expanded ISAF Meeting and also meet various heads of state and government on the sidelines of the NATO Summit. He will be accompanied by Foreign Minister Hina Rabbani Khar and Foreign Secretary Jalil Abbas Jilani. The NATO Secretary General telephoned President Zardari Tuesday and invited him to the NATO summit, presidential spokesman said. Prime Minister Yusuf Raza Gilani said the invitation to the NATO summit was unconditional and not linked to the reopening of ground lines of communication for NATO or to any other issue. The NATO Secretary General suggested last Friday that Pakistan could miss out on important talks on the future of Afghanistan if it failed to reopen the supply routes in time to secure a place at the NATO summit. Pakistan blocked the supply lines for NATO-led forces in Afghanistan after 24 soldiers were killed in a NATO cross-border air strike last November. Senior military and civil leaders have made a decision to reopen the supply routes amid growing U.S. pressure but delayed a formal announcement, official sources said. The sources said that invitation to the NATO summit was extended to Pakistan after the officials conveyed to the U.S. about the decision to unblock the supply routes.