Suramarit, Sihanouk's father, died on 3 April 1960 after several months of poor health that Sihanouk blamed upon the shock that his father had received from the parcel bomb attack.
The following day, the Cambodian Crown Council met to choose Monireth as regent.
Over the next two months, Sihanouk introduced constitutional amendments to create the new post of Head of State of Cambodia, which provided ceremonial powers equivalent to that of the king.
A referendum held on 5 June 1960 approved Sihanouk's proposals, and Sihanouk was formally appointed Head of State on 14 June 1960.
As the head of state, Sihanouk took over various ceremonial responsibilities of the king, such as holding public audiences and leading the Royal Ploughing Ceremony.
At the same time, he continued to play an active role in politics as Sangkum's leader.

In 1961 Pracheachon's spokesperson, Non Suon, criticized Sihanouk for failing to tackle inflation, unemployment, and corruption in the country.
Non Suon's criticisms gave Sihanouk the impetus to arrest Pracheachon leaders, and, according to him, he had discovered plans by their party to monitor local political developments on behalf of foreign powers.
In May 1962 Tou Samouth, Pracheachon's secretary-general, disappeared, and its ideological ally, the Communist Party of Kampuchea, suspected that Samouth had been secretly captured and killed by police.
Sihanouk nevertheless allowed Sangkum's left-wing politicians to run again in the 1962 general elections, which they all won.
He even appointed two left-wing politicians, Hou Yuon and Khieu Samphan, as secretaries for planning and commerce, respectively, after the election.

In November 1962, Sihanouk called on the US to stop supporting the Khmer Serei, which he believed they had been secretly doing through the CIA.
He threatened to reject all economic aid from the US if they failed to respond to his demands, a threat he later carried out on 19 November 1963.
At the same time, Sihanouk also nationalised the country's entrepot trade, banking sector, and distillery industries.
To oversee policy and regulatory matters on the country's entrepot trade, he set up the National Export-Import Corporation and Statutory Board, better known as "SONEXIM".
When Sarit, Diem, and US president John F. Kennedy died in November and December 1963, Sihanouk rejoiced over their deaths, as he accused them of attempting to destabilise Cambodia.
He organised concerts and granted civil servants extra leave time to celebrate the occasion.
When the US government protested Sihanouk's celebrations, he responded by recalling the Cambodian ambassador to the US, Nong Kimny.

In early 1964, Sihanouk signed a secret agreement with North Vietnam and the Viet Cong, allowing Chinese military aid meant for them to be delivered through Sihanoukville's port.
In turn, the Cambodian army would be paid for delivering food supplies to the Viet Cong, and at the same time skim off 10 percent of all military hardware supplies.
In addition, he also allowed the Viet Cong to build a trail through eastern Cambodia, so that their troops could receive war supplies from North Vietnam.
The trail later became known as the Sihanouk Trail.
When the US learned of Viet Cong presence in eastern Cambodia, they started a bombing campaign, spurring Sihanouk to sever diplomatic ties with the US in May 1965.
As a result of this secret agreement, Communist countries, including China, the Soviet Union, and Czechoslovakia, provided military aid to Cambodia.
Suramarit, Sihanouk's father, died on 3 April 1960 after several months of poor health that Sihanouk blamed upon the shock that his father had received from the parcel bomb attack. The following day, the Cambodian Crown Council met to choose Monireth as regent. Over the next two months, Sihanouk introduced constitutional amendments to create the new post of Head of State of Cambodia, which provided ceremonial powers equivalent to that of the king. A referendum held on 5 June 1960 approved Sihanouk's proposals, and Sihanouk was formally appointed Head of State on 14 June 1960. As the head of state, Sihanouk took over various ceremonial responsibilities of the king, such as holding public audiences and leading the Royal Ploughing Ceremony. At the same time, he continued to play an active role in politics as Sangkum's leader.
In 1961 Pracheachon's spokesperson, Non Suon, criticized Sihanouk for failing to tackle inflation, unemployment, and corruption in the country. Non Suon's criticisms gave Sihanouk the impetus to arrest Pracheachon leaders, and, according to him, he had discovered plans by their party to monitor local political developments on behalf of foreign powers. In May 1962 Tou Samouth, Pracheachon's secretary-general, disappeared, and its ideological ally, the Communist Party of Kampuchea, suspected that Samouth had been secretly captured and killed by police. Sihanouk nevertheless allowed Sangkum's left-wing politicians to run again in the 1962 general elections, which they all won. He even appointed two left-wing politicians, Hou Yuon and Khieu Samphan, as secretaries for planning and commerce, respectively, after the election.
In November 1962, Sihanouk called on the US to stop supporting the Khmer Serei, which he believed they had been secretly doing through the CIA. He threatened to reject all economic aid from the US if they failed to respond to his demands, a threat he later carried out on 19 November 1963. At the same time, Sihanouk also nationalised the country's entrepot trade, banking sector, and distillery industries. To oversee policy and regulatory matters on the country's entrepot trade, he set up the National Export-Import Corporation and Statutory Board, better known as "SONEXIM". When Sarit, Diem, and US president John F. Kennedy died in November and December 1963, Sihanouk rejoiced over their deaths, as he accused them of attempting to destabilise Cambodia. He organised concerts and granted civil servants extra leave time to celebrate the occasion. When the US government protested Sihanouk's celebrations, he responded by recalling the Cambodian ambassador to the US, Nong Kimny.
In early 1964, Sihanouk signed a secret agreement with North Vietnam and the Viet Cong, allowing Chinese military aid meant for them to be delivered through Sihanoukville's port. In turn, the Cambodian army would be paid for delivering food supplies to the Viet Cong, and at the same time skim off 10 percent of all military hardware supplies. In addition, he also allowed the Viet Cong to build a trail through eastern Cambodia, so that their troops could receive war supplies from North Vietnam. The trail later became known as the Sihanouk Trail. When the US learned of Viet Cong presence in eastern Cambodia, they started a bombing campaign, spurring Sihanouk to sever diplomatic ties with the US in May 1965. As a result of this secret agreement, Communist countries, including China, the Soviet Union, and Czechoslovakia, provided military aid to Cambodia.
Norodom Sihanouk