"We regret today's incident. There may have been civilians among the protesters who came to protest peacefully, but may have been

exploited

by others. We stress that while we try to be accommodating, we may have to use force to protect the state and its

prestige

."

American military trainers have returned to Yemen to help counter recent gains by al-Qaeda militants and their supporters. Washington said a number of US personnel were working with the Yemeni armed forces. It didn't disclose the precise nature of their work or how many of them were involved.

The leader of the far-left Syriza group in Greece, Alexis Tsipras, has urged the country's two traditional big parties to abandon their commitment to austerity, saying voters had rejected it in Sunday's election. Mr Tsipras has been three days to try to form a coalition government. Here's our Athens correspondent Mark Lowen.

"Mr Tsipras, will you succeed in forming a government?"

There was no answer from Greece's young leftist leader as he entered the

presidency

building, given a mandate to attempt to form a new coalition here. Alexis Tispras has now begun talks with a range of parties – mainly from the left – but on one condition that Greece's international bailout and the austerity measures that accompany it are

torn up

. The likelihood of now forming a government is fading fast with a probability of fresh elections. That would hold up the next installment of the country's loan, and again raise the spectre of Greece's bankruptcy.