Tens of thousands of anti-government protesters gathered in Pakistan's capital Islamabad in the pouring rain following the arrival of convoys led by a cricket star-turned-politician and a fiery anti-Taliban cleric.

The protests led by Imran Khan and cleric Tahir-ul-Qadri represent the biggest challenge yet to prime minister Nawaz Sharif's government.

Security had been tightened across the capital amid fears of unrest. Both Mr Khan and Mr Qadri have vowed to bring one million of their followers into the streets of Islamabad.