(CNN) -- Former interim Thai Prime Minister Niwatthamrong Boonsongpaisan is among the latest batch of people that the military has released following last week's coup, a military officer said Thursday.
Also among the 31 people recently released was former Thai Foreign Minister Surapong Tovichakchaikul, Col. Sirichan Ngathong told reporters.
The military had summoned, and in some cases detained, scores of political officials and other prominent figures after the May 22 coup, which the military carried out after months of unrest that had destabilized the elected government and caused outbursts of deadly violence in Bangkok.
But the sudden intervention by the armed forces -- the latest in a series of coups that have punctuated modern Thai history -- has been criticized by human rights activists and foreign governments, including the United States.
Small groups of protesters also have gathered in Bangkok in recent days, with demonstrators calling for democratic elections. But security forces sealed off one of the main protest sites -- a monument -- on Thursday, days after the officer who led the coup suggested that the military wouldn't tolerate public displays of dissent indefinitely.
Boonsongpaisan was interim prime minister when the military conducted the coup. The military, which tore up the country's constitution and declared martial law, says it so far has summoned at least 280 people, and about 200 of them -- including former Prime Minister Yingluck Shinawatra -- turned themselves in.
The military says it has released about 155 people so far, including Yingluck, who was in office when the current phase of political turmoil began in November.
Yingluck, who was removed from office by the courts earlier this month, was released from a military facility over the weekend after she followed a summons to report to military authorities on Friday.
A military source said Yingluck was asked to "help us maintain peace and order and not to get involved with protesters or any political movement" and now has freedom of movement and communication. But a close aide to Yingluck disagreed with the assertion that she was free to move and communicate.
The military has said it would impress upon the summoned people the negative consequences their actions have had for the country in the sometimes bloody conflict of the last seven months.
Detainees determined to have no significant link to conflict and who find "common ground" for the good of the country will be released, a military spokesman previously said.
The recent unrest was driven by months of protests against Yingluck's government.
The protest leaders said they wanted to rid Thailand of the influence of Yingluck and her wealthy brother, the exiled former Prime Minister Thaksin Shinawatra, who was deposed in the country's last military coup in 2006.
The siblings' powerful political movement, which has dominated elections for more than a decade, draws its support from Thailand's populous rural regions in the north and northeast.
But it is unpopular among the Bangkok elites, who accuse it of buying votes through ill-judged, populist policies.
The protesters who campaigned against Yingluck's government claimed Thailand needed reforms to be imposed by an unelected council before any further elections could take place.
With the military's intervention, they appear to have gotten their wish, although some of the protest leaders were taken into custody after the coup.
On Monday, the officer who led the coup, Gen. Prayuth Chan-ocha told reporters there was "no set time period" for when new elections might be held, and he outlined the steps he said his junta plan to take, including setting up a committee to introduce reforms.
CNN's Paula Hancocks, Jethro Mullen and journalist Kiki Dhitavat contributed to this report.