Fri Sep 28, 7:58 AM ET

LONDON - Prime Minister Gordon Brown said Friday that violence against demonstrators in Myanmar "must cease," condemning the military regime and saying the coming days will be critical.

"I had hoped that the Burmese regime would heed the calls for restraint from the international community. But once again they have responded with oppression and force. This must cease," he said in a statement.

His comments came after Myanmar security forces again fired warning shots and launched baton charges on protesters, trying to quell the biggest demonstrations against the junta in 20 years.

At least 13 people have been killed since the crackdown began Wednesday.

"The coming days will be critical. The international community must intensify its efforts," said Brown.

"The UK is pressing urgently for tougher EU sanctions. We strongly back the mission of Ban Ki-moon's representative, Ibrahim Gambari, to Burma. I applaud the powerful call for restraint from the countries of ASEAN," he said.

He added that he would be speaking to Chinese Prime Minister Wen Jiabao and US President George W. Bush later in the day about the situation.