WASHINGTON (Reuters) - U.S. President Joe Biden on Sunday congratulated Turkish President Tayyip Erdogan on winning the second round in Turkey's presidential election, one of the most consequential in the country's modern history.

"I look forward to continuing to work together as NATO Allies on bilateral issues and shared global challenges," Biden said in a tweet.

Biden's NATO emphasis reflects Washington's priority in seeing Sweden join NATO by the Vilnius summit in mid-July.

Finland joined NATO last month, but Sweden's membership has been held up by objections from Turkey and Hungary. Turkey says Stockholm harbors members of militant groups it considers to be terrorists.

The hold-up of NATO enlargement is not the only thorn in the bilateral relationship between Washington and Ankara.

The two NATO allies disagree over a host of issues including Syria policy, Ankara's close relationship with Moscow and the potential sale of U.S.-made F-16 fighter jets to Turkey - issues analysts expect to continue to muddy ties.

(Reporting by Humeyra Pamuk and Daphne Psaledakis; Editing by Howard Goller)