British cargo planes have dropped water and solar lamps to thousands of people trapped on Mount Sinjar in northern Iraq since fleeing advancing Islamic militant forces.

The Department for International Development said Tuesday it was Britain's second drop to help besieged Yazidis sheltering on the mountain. An earlier drop had to be aborted because the Royal Air Force feared injuring the crush of desperate people below.

There is increasing pressure on Prime Minister David Cameron to take more vigorous action in Iraq.

Downing Street says it will send Tornado jets to the region so they can be used if necessary for surveillance. Britain says it will also see if it can play a role in helping equip Kurdish forces.