it would pollute the environment and lead to diplomatic tensions between the two countries. The ensuing dispute remained a subject of controversy into 2010, particularly after ongoing reports of increased water contamination in the area were later proven to be from sewage discharge from the town of Gualeguaychú in Argentina. In November 2010, Uruguay and Argentina announced they had reached a final agreement for joint environmental monitoring of the pulp mill. Brazil and Uruguay have signed cooperation agreements on defence, science, technology, energy, river transportation and fishing, with the hope of accelerating political and economic integration between these two neighbouring countries. Uruguay has two uncontested boundary disputes with Brazil, over Isla Brasilera and the Invernada River region near Masoller. The two countries disagree on which tributary represents the legitimate source of the Quaraí/Cuareim River, which would define the border in the latter disputed section, according to the 1851 border treaty between the two countries. However, these border disputes have not prevented both countries from having friendly diplomatic relations and strong economic ties. So far, the disputed areas remain de facto under Brazilian control, with little to no actual effort by Uruguay to assert its claims. Uruguay has enjoyed friendly relations with the United States since its transition back to democracy. Commercial ties between the two countries have expanded substantially in recent years, with the signing of a bilateral investment treaty in 2004 and a Trade and Investment Framework Agreement in January 2007. The United States and Uruguay have also cooperated on military matters, with both countries playing significant roles in the United Nations Stabilization Mission in Haiti. President Mujica backed Venezuela's bid to join Mercosur. Venezuela had a deal to sell Uruguay up to 40,000 barrels of oil a day under preferential terms. On 15 March 2011, Uruguay became the seventh South American nation to officially recognize a Palestinian state, although there was no specification for the Palestinian state's borders as part of the recognition. In statements, the Uruguayan government indicated its firm commitment to the Middle East peace process, but refused to specify borders "to avoid interfering in an issue that would require a bilateral agreement". In 2017, Uruguay signed the UN treaty on the Prohibition of Nuclear Weapons. In March 2020, Uruguay rejoined the Inter-American Treaty of Reciprocal Assistance (TIAR or "Rio Pact"). In September 2019, the previous left-wing government of Uruguay had withdrawn from TIAR as a