Every time a U.S. company issues securities, it must do so in compliance with federal and state securities laws. If foreign investors are "accredited investors", then a U.S. company can issue them securities pursuant to Rule 506 (assuming all other requirements of Rule 506 are met), just as it would issue securities to U.S. investors.
If a foreign investor is not an accredited investor, the company may still be able to issue securities to that investor under Regulation S. Regulation S requires, among other things, that the issuance of securities comply with the laws of the investor's country. You should discuss with competent securities counsel before issuing securities to foreign investors.