KAMPALA (Reuters) - Ugandan police gave a second opposition lawmaker approval on Monday to travel abroad for medical treatment after he said he had been tortured in custody, but they also charged him with treason, his lawyer said.

The capital Kampala was rocked by protests on Friday after Francis Zaake and Robert Kyagulanyi, a pop singer turned lawmaker better known by his stage name of Bobi Wine, had been prevented from leaving the country.

Zaake was now on his way to the airport to travel to India for treatment, lawyer Nicholas Opiyo told Reuters.

Kyagulanyi arrived in the United States already on Saturday after authorities in Uganda - an ally of the West which has welcomed foreign investors but is faced with accusations of human rights abuses - eventually allowed him to leave.

Ugandan authorities have rejected the accusations of torture by both men but said they would investigate them.

On Monday, Kyagulanyi published a long and detailed account of what he said was the torture he was submitted to.

“They beat me, punched me, and kicked me with their boots. No part of my body was spared. They hit my eyes, mouth and nose. They hit my elbows and my knees. Those guys are heartless!” he said, in a detailed, and sometimes gruesome account of his detention.

Kyagulanyi, who entered politics after winning a parliamentary by-election last year, has emerged as a formidable threat to the 32-year rule of President Yoweri Museveni.

Kyagulanyi, Zaake and three other lawmakers were detained on Aug. 13 in the northwestern town of Arua, accused of throwing stones at Museveni’s convoy during the campaign for a parliamentary seat. All five lawmakers have rejected the accusation.

“The police have charged ... Zaake with treason and unlawful escape & bonded him for a month to allow him travel for medical treatment,” Opiyo said on Twitter earlier.

Government officials were not immediately available for comment.

Kyagulanyi has amassed a large following among youth electrified by his scathing criticism of Museveni, sometimes delivered in his songs.

Museveni has won praise in the West for his opposition to militant Islam in the region, but many Ugandans regard the 73-year-old as out of touch with his people, nearly 80 percent of whom are under the age of 30.

He has been in power since 1986 and has repeatedly been accused by his opponents of rights abuses and the widespread use of security forces to suppress opposition to his rule. He denies charges that his government is involved in rights violations.

Uganda has welcomed foreign investors such as France’s Total, China’s CNOOC and Britain’s Tullow as part of a plan to start pumping oil from 2021.