KABUL, July 19 (Reuters) - A wanted rebel leader in Afghanistan, Gulbuddin Hekmatyar, has declared a ceasefire against the government, a statement signed by Hekmatyar said. The statement, aired by a private television and circulated in Kabul, said: "Members of Hezb-i-Islami have stopped and refrained from brother killing and from the destruction of the country and assumed political activity," the statement said.