Before the final integration of 1,500 Pathet Lao troops (two battalions) into the Royal Lao Army could take place as planned in May 1959, the Pathet Lao used a quibble about officer ranks to delay the final ceremony. As monsoon rains swept over the Plain of Jars one night, one of the two battalions slipped away, followed soon after by the other, near Louangphrabang. The event signaled a resumption of hostilities. In July Phoui's government, after protracted cabinet deliberations, ordered the arrest of the Lao Patriotic Front (LPF) deputies in Vientiane.
Fighting broke out all along the border with North Vietnam. North Vietnamese regular army units participated in attacks on July 28-31, 1959. These operations established a pattern of North Vietnamese forces leading the attack on a strong point, then falling back and letting the Pathet Lao remain in place once resistance to the advance had been broken. The tactic had the advantage of concealing from view the North Vietnamese presence. Rumors of North Vietnamese in the vicinity often had a terrifying effect on Royal Lao Army forces, however.
A split in the Royalist camp emerged in the summer of 1960. A neutralist coup, led by Kong Le, followed by Thai and American supported resistance from rightists, led by Phoumi, created a realignment of forces in the civil war that benefited the Pathet Lao. The only offensive actions taken by Royal Lao Army troops against the Pathet Lao between August and December 1960 were those taken by troops loyal to Souvanna Phouma, and supported by Kong Le and nominally the Pathet Lao, in Phôngsali and elsewhere.
Phoumi's failure to advance on the Plain of Jars, in December 1960, against forces of Kong Le supported by the Pathet Lao and North Vietnamese, made a deep impression on the new administration of United States president John F. Kennedy. If Phoumi had his difficulties with Kong Le's outnumbered battalion, he was no match for the North Vietnamese. The North Vietnamese-Pathet Lao counteroffensive that opened in January 1961 drove Phoumi's poorly motivated troops and their United States military advisers back--a retreat that irrevocably changed the balance of forces in Laos. Central Laos and the entire length of the road from the Sala Phou Khoun junction south to Vangviang was in North Vietnamese-Pathet Lao hands by mid-March 1961.
The Royal Lao Army had been quietly supplying arms to the Hmong since at least March 1957 to enable them to resist the Pathet Lao, but the North Vietnamese influx created a sudden need for arms far in excess of what the Laotians could supply, even with the help of Thailand. The Hmong, under their military leader Vang Pao, had taken up positions in the mountains surrounding the Plain of Jars and asked to talk to United States officials. Vang Pao requested quick delivery of arms, but United States officials were concerned that the Hmong would not fight, and the arms might fall into communist hands. Vang Pao said all 7,000 volunteers would fight, but they needed the arms in three days or they would have to fall back to less exposed positions. United States airdrops of arms from stocks in Okinawa began three days later, signaling the beginning of a heroic Hmong resistance.
Contact between emissaries of the two sides was finally made by officers under a truce flag at the village of Ban Hin Heup on the Vientiane-Louangphrabang road. Tripartite truce talks opened in the nearby village of Ban Namone, with the ICC, reconvened by the cochairmen of the Geneva Conference, Britain, and the Soviet Union, present. A cease-fire was declared on May 3, 1961.