Concern is growing for tens of thousands of refugees on the Syrian-Jordanian border after Amman blocked access to a makeshift refugee camp following last week's deadly jihadist attack at the frontier.

A Jordanian court on Sunday charged 21 people with carrying out "terrorist acts" after their arrest in an operation against jihadists in the country's north in March, a prosecutor said.

The Islamic Action Front, the political arm of Jordan's Muslim Brotherhood, said on Sunday it will take part in September parliamentary elections which it had boycotted in 2010 and 2013.

Jordan's King Abdullah II vowed on Tuesday to act decisively against anyone who threatens the kingdom's security, a day after a lone gunman shot dead five intelligence officers.

A gunman apparently acting alone killed five Jordanian intelligence agents on Monday in a daylight "terrorist attack" on their office in a Palestinian refugee camp north of the capital.

Jordan is a leading member of the U.S.-led coalition fighting the Islamic State group in neighboring Iraq and Syria, and has been the target of jihadist attacks in the past.

Jordan's new Prime Minister Hani Mulki formed his government on Wednesday to prepare for legislative elections following the dissolution of parliament, the royal palace announced.

The 65-year-old, who has held several ministerial posts, is expected to push for business-friendly policies to revive Jordan's lagging economy.

Human Rights Watch urged Jordan Monday to lift recent "restrictions" on transit through its territory of Palestinians from the Gaza Strip, but the authorities in Amman denied any policy change.

Since August 2015, "Palestinians from Gaza have found it increasingly difficult to get permission to transit through Jordan to travel abroad, without any explanation for the change," HRW's Middle East director Sarah Leah Whitson wrote in a letter to the Jordanian authorities.

Around 64,000 Syrians are stranded at the border with Jordan after intensified violence around Aleppo, Jordanian border guards said on Thursday.

The kingdom, which is already home to more than 630,000 Syrian refugees, introduced additional security checks at the Hadalat and Rokbane border crossings at the start of the year, leading tens of thousands more to congregate along the frontier.

Around 50,000 Syrians are stranded in no-man's land along the border with Jordan, a three-fold increase since January because of increased security checks, state news agency Petra reported Monday.

The agency, quoting government spokesman Mohamed Momani, said the estimated 50,000 refugees were massed around the desert border posts of Hadalat and Rokban.

Jordan on Monday summoned its ambassador in Iran for consultations over what Amman said was the Islamic republic's "meddling in Arab affairs," a government spokesman said.

Mohamed Momani, who is also the kingdom’s information minister, said Jordan's envoy would return to Amman for "discussions".