(Updates peso prices in ninth paragraph) BUENOS AIRES, July 12 (Reuters) - Argentina’s securities regulator tightened rules on some bond trades on Monday, lowering a weekly limit on trading of local and international bonds amid a wider clampdown on alternative channels used to access foreign exchange. The measure from the National Securities Commission (CNV), published in the official gazette, halved the cap on weekly trades per account to 50,000 local law bonds and to the same level for international law bonds. In an easing move, it reduced the amount of time traders must hold the securities before reselling them to two business days, from three days previously, for “negotiable securities with settlement in foreign currency and in a foreign jurisdiction”. Sales with foreign currency settlement but in the local jurisdiction would face a single-day holding period. Many companies and individuals in the South American nation access dollars via legal, though unofficial, roundabout routes that often involve processes of buying and then selling financial assets, including bonds, in Argentina and abroad. These alternative foreign exchange markets have become increasingly popular due to tough capital controls imposed since 2019, which have created parallel exchange rates that have diverged sharply from the official peso-dollar rate. “The CNV measures constitute another turn of the screw,” said Roberto Geretto, a local economist at Fundcorp, adding that the aim was to lower the volume of trades in parallel foreign exchange markets. On Saturday, Argentina’s central bank tightened rules on companies accessing dollars in alternative foreign exchange markets. On Monday the so-called Blue Chip Swap rate gained 0.4% to 166.7 per dollar after initially weakening, while the black market peso fell 2.7% to 174 per dollar in thin trading, its weakest level since October. The official rate edged down to 96.1 per dollar. Argentina’s central bank has been trying to rebuild depleted foreign currency reserves and has purchased some $6.7 billion so far in 2021, according to official data until July 5. Those reserves are key with the country locked in talks to revamp some $45 billion it owes to the International Monetary Fund. Argentines have long flocked to the safe-haven of dollars, with rampant inflation - currently near 50% on an annual basis - and regular economic crises weighing on the local peso currency. (Reporting by Hernan Nessi and Walter Bianchi Editing by Paul Simao and Alistair Bell) Our Standards: The Thomson Reuters Trust Principles.