Kenyan President Uhuru Kenyatta's first year in office has been marked by a string of "worrisome cases" of rights infringements and by rampant impunity, two rights groups said in a report Wednesday.

The Kenya Human Rights Commission( KHRC) and the International Federation of Human Rights (FIDH) said Kenyan authorities "have attempted to clamp down on dissenting voices, either through the adoption of restrictive legislation aimed at further regulating the NGO or media sectors."

The U.N. refugee agency said Thursday it was "disturbed by reports of harassment and other abuses" in a Kenyan counter-terrorism operation targeting Somalis that has seen thousands arrested and scores expelled.

Conditions in a sports stadium being used as a giant holding pen and in police stations are "overcrowded and sanitary conditions are inadequate," the UNHCR said in a statement, adding that 82 Somalis had been deported back to their war-torn country.

The group of Islamist gunmen who stormed the Westgate shopping mall in Nairobi last year, killing at least 67 people, may have entered Kenya from neighboring Uganda, a senior police official was quoted as saying Saturday.

Uganda's police chief, General Kale Kayihura, cited intelligence reports indicating that Uganda had been used as a transit stage. He added that Uganda was also still at risk of attack.

Kenya's defence ministry said Friday its troops had freed two Kenyans kidnapped near its northern border by Somalia's al-Qaida-linked Shebab rebels in 2011.

Officials identified the two as James Kiarie Gichuhi, a driver with CARE International, and Daniel Njuguna Wanyoike, initially identified as a worker with Doctors Without Borders (MSF) but later said to be working with a logistics firm that may have been delivering medicines to the charity.

Kenya's opposition party on Thursday slammed the mass round-up and deportation of ethnic Somalis by police after a week-old counter-terrorism crackdown saw 4,000 people arrested.

The latest sweep, conducted in Nairobi's main Somali district Eastleigh since last Friday, is aimed at weeding out sympathizers of the al-Qaida-linked Shebab, but residents say people of Somali origin have been rounded up indiscriminately.

Dozens of Somalis were expelled from Kenya on Wednesday, officials said, as security forces maintained a major crackdown on suspected Islamists that has seen thousands rounded up in the capital.

Kenya's Interior Minister Joseph Ole Lenku said 3,000 people have so far been detained in the operation, and 82 of them flown back to Somalia's Mogadishu. He said hundreds more were still undergoing identity checks.

Kenyan security forces have rounded up thousands of Somalis or Kenyans of Somali origin, leaving many languishing in a football stadium, amid a major crackdown on suspected Islamists blamed for a string of attacks.

The operation, which local media say has involved more than 6,000 men from the police and from the elite General Service Unit, started on Friday and appeared to have been focused on Eastleigh, an ethnic Somali-dominated district of the Kenyan capital.

A Venezuelan diplomat reappeared briefly in court in Kenya on Monday on charges of killing his country's ambassador in July 2012, although the case was adjourned to early June.

Venezuela's former first secretary to Kenya, Dwight Sagaray, is charged alongside several other accused.

Kenyan police and Muslim youths clashed in Mombasa following Friday prayers, witnesses said, days after a firebrand Islamist cleric was gunned down in the port city.

Security was tight and tensions high around the Musa mosque, seen by Kenyan authorities as a terrorist propaganda hub and recruiting ground for jihadists.

Kenya must carry out a thorough investigation into this week's murder of a firebrand Muslim cleric in the port city of Mombasa or else risk an escalation of religious violence, Human Rights Watch said Friday.

Abubaker Shariff Ahmed, better known as Makaburi and a vocal supporter of Osama bin Laden and Al-Qaeda, was gunned down in the strategic city on Tuesday. Prior to his death he had accused Kenyan security forces of seeking to kill him.