An explosion in a busy vegetable market killed at least 21 people on Saturday in Pakistan's remote northwestern tribal region of Kurram near the border with Afghanistan.   About 40 others were also wounded in the said blast. The blast happened in a crowded vegetable market in Parachinar city, the capital of Kurram tribal district which is a mainly Shiite area. It is reported that the blast was caused by an IED (improvised explosive device) which was hidden in a vegetable box. Army helicopters are used to evacuate the injured people. A probe has been ordered.